Method and apparatus for allocating channel state information-reference signal in wireless communication system

ABSTRACT

Disclosed are an apparatus for Channel State Information-Reference Signal (CSI-RS) allocation and a method for CSI-RS transmission using the same in a wireless communication system. A CSI-RS for each antenna port is allocated to REs or subcarriers on a basis of a symbol or symbol axis in a subframe or Resource Block (RB), and is allocated in such a manner that a distance between neighboring CSI-RS allocation REs or subcarriers may be 3 REs or subcarriers. Accordingly, in the range of following CSI-RS transmission overhead, CSI-RSs are allocated to a time-frequency resource domain in such a manner so as to have perfect orthogonality or quasi-orthogonality according to cells or cell groups. Then, the CSI-RSs, which have been allocated to the time-frequency resource domain, are transmitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/192,233, filed on Jun. 24, 2016, which is a continuation of U.S.patent application Ser. No. 14/464,041, filed on Aug. 20, 2014, which isa continuation of U.S. patent application Ser. No. 14/043,005, filed onOct. 1, 2013, issued as U.S. Pat. No. 8,837,452, which is a continuationof U.S. patent application Ser. No. 13/008,685, filed on Jan. 18, 2011,and issued as U.S. Pat. No. 8,576,822, and claims priority from andclaims the benefit of and priority from Korean Patent Application No.10-2010-0004219, filed on Jan. 18, 2010, all of which are herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND

Field

Exemplary embodiments of the present invention relate to a wirelesscommunication system, and more particularly to a method and an apparatusfor allocating a Channel State Information-Reference Signal (CSI-RS)between cells in a wireless communication system.

Discussion of the Background

With the development of communication systems, consumers, includingbusiness companies and individuals, require wireless communicationterminals supporting various services.

Current mobile communication systems, such as 3GPP (3rd GenerationPartnership Project), LTE (Long Term Evolution), and LTE-A (LTEAdvanced), are resulting in the development of technology for ahigh-speed large-capacity communication system, which can transmit orreceive various data, such as images and wireless data, beyond thecapability of providing a voice service, and can transmit data of such alarge capacity as that transmitted in a wired communication network.Moreover, the current mobile communication systems require a propererror detection scheme, which can decrease the reduction of informationloss and improve the system transmission efficiency, thereby improvingthe system performance.

Further, for the current wide variety of communication systems, variousreference signals have been and are being proposed in order to providecounterpart apparatuses with information on a communication environment,etc., through a downlink or an uplink.

For example, in the LTE system, a Cell-specific Reference Signal (CRS),which is a reference signal, is transmitted at each sub-frame.

At this time, since the maximum number of antenna ports supportable inthe downlink of the LTE system is four, CRSs are allocated to andtransmitted through a maximum of four antennas according to thetime/frequency.

Meanwhile, the next generation communication technologies, such as theLTE-A, which is being currently developed, can support a maximum ofeight antennas. Therefore, the current CRSs defined for only fourexisting antennas are insufficient for detection of channel informationat the time of downlink transmission. To this end, a technology forobtaining channel state information of a maximum of eight antennas bynewly defining a reference signal named “Channel StateInformation-Reference Signal (CSI-RS)” is being discussed.

In other words, a communication system using a maximum of eight MultipleInput Multiple Output (MIMO) antennas at each of the transmission portand the reception port is being discussed, and a scheme of transmittingCSI-RSs discriminated according to the antenna ports or antenna layersfor the transmission or reception thereof is being discussed. However,up to the present, only basic definitions for the CSI-RS and definitionsfor the overhead problem have been arranged, and definitions for CSI-RSallocation and transmission have not been arranged. In this regard, thenext generation wireless communication systems are requiring a specificscheme for the CSI-RS allocation and transmission.

SUMMARY

Exemplary embodiments of the present invention provide a scheme fordefining a CSI-RS pattern for each antenna/base station (cell),allocating the CSI-RS to resource areas, and transmitting the CSI-RS.

Exemplary embodiments of the present invention provide an apparatus anda method for allocating a Channel State Information-Reference Signal(CSI-RS) to a time-frequency resource area for each antenna port in awireless communication system.

Exemplary embodiments of the present invention provide an apparatus anda method for allocating a CSI-RS to a time-frequency resource area so asto enable each cell to have an orthogonality or a quasi-orthogonality ina wireless communication system.

Exemplary embodiments of the present invention provide an apparatus anda method for allocating a CSI-RS for each antenna port, which enableeach cell (or group) to have a frequency shift in a wirelesscommunication system.

Exemplary embodiments of the present invention provide an apparatus anda method for allocating a CSI-RS, which can decrease performancedegradation due to interference between neighbor cells in a wirelesscommunication system.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

An exemplary embodiment of the present invention provides a method fortransmitting a Channel State Information-Reference Signal (CSI-RS), themethod including: generating a CSI-RS sequence for an antenna port fortransmission of a maximum of N (N being an integer larger than or equalto 1) number of CSI-RSs; mapping the generated CSI-RS sequence toResource Elements (REs) allocated for transmission of the CSI-RS; andgenerating an Orthogonal Frequency Division Multiplexing (OFDM) signalincluding information on the mapped CSI-RS sequence and transmitting thegenerated OFDM signal to a reception apparatus, wherein, in mapping thegenerated CSI-RS sequence to the REs, the CSI-RS sequence is mapped toREs corresponding to one sub-carrier at every 12 sub-carriers withrespect to two OFDM symbols or symbol axes for each antenna port withina particular sub-frame by which the CSI-RS is transmitted, for a totalof ┌N/2┐ antenna port sets, each of which includes either both an M^(th)(M≤N, and M being an odd number) antenna port and an (M+1)^(th) antennaport or only the M^(th) antenna port if the (M+1)^(th) antenna port doesnot exist and is used as an antenna port set for transmission of oneCSI-RS, a CSI-RS of antenna ports within each of the antenna port setsis allocated to REs having the same time-frequency resource and arediscriminated from each other by orthogonal codes, and the CSI-RSallocated REs of different antenna port sets adjacent to each other inthe frequency axis are spaced apart from each other with an interval of3 REs.

An exemplary embodiment of the present invention provides a method fortransmitting a Channel State Information-Reference Signal (CSI-RS), themethod including: generating a CSI-RS sequence for an antenna port fortransmission of a maximum of 8 CSI-RSs; mapping the generated CSI-RSsequence to Resource Elements (REs) allocated for transmission of theCSI-RS; and generating an Orthogonal Frequency Division Multiplexing(OFDM) signal including information on the mapped CSI-RS sequence andtransmitting the generated OFDM signal to a reception apparatus,wherein, in mapping the generated CSI-RS sequence to the REs, the CSI-RSsequence is mapped to REs corresponding to one sub-carrier at every 12sub-carriers with respect to two OFDM symbols or symbol axes for eachantenna port within a particular sub-frame by which the CSI-RS istransmitted, for a total of four antenna port sets, each of whichincludes either both an M^(th) (M=1, 3, 5, 7) antenna port and an(M+1)^(th) antenna port or only the M^(th) antenna port if the(M+1)^(th) antenna port does not exist and is used as an antenna portset for transmission of one CSI-RS, a CSI-RS of antenna ports withineach of the antenna port sets is allocated to REs having the sametime-frequency resource and are discriminated from each other byorthogonal codes, and the CSI-RS allocated REs of different antenna portsets adjacent to each other in the frequency axis are spaced apart fromeach other with an interval of 3 REs.

An exemplary embodiment of the present invention provides a method forreceiving a CSI-RS, the method including: receiving a transmittedsignal; extracting CSI-RS information for each of multiple antenna portsallocated to a particular Resource Element (RE) through resource elementdemapping of the received signal; and acquiring channel stateinformation from the extracted CSI-RS information, wherein, in thetransmitted signal, for an antenna port for transmission of a maximum ofN (N being an integer larger than or equal to 1) number of CSI-RSs, theCSI-RS sequence is mapped to REs corresponding to one sub-carrier atevery 12 sub-carriers with respect to two Orthogonal Frequency DivisionMultiplexing (OFDM) symbols or symbol axes for each antenna port withina particular sub-frame by which the CSI-RS is transmitted, for a totalof ┌N/2┐ antenna port sets, each of which includes either both an M^(th)(M≤N, and M being an odd number) antenna port and an (M+1)^(th) antennaport or only the M^(th) antenna port if the (M+1)^(th) antenna port doesnot exist and is used as an antenna port set for transmission of oneCSI-RS, a CSI-RS of antenna ports within each of the antenna port setsis allocated to REs having the same time-frequency resource and arediscriminated from each other by orthogonal codes, and the CSI-RSallocated REs of different antenna port sets adjacent to each other inthe frequency axis are spaced apart from each other with an interval of3 REs.

An exemplary embodiment of the present invention provides a method fortransmitting a CSI-RS, the method including: generating a CSI-RS foreach of a maximum of 8 antenna ports; allocating a CSI-RS of an antennaport to four Resource Elements (REs) or sub-carriers based on a unit ofone symbol (or symbol axis) in a time-frequency resource area within onesub-frame in such a manner that adjacent CSI-RS allocated REs orsub-carriers have an interval of 3 REs or sub-carriers therebetween; andtransmitting the CSI-RS allocated to the time-frequency resource area toa reception apparatus.

An exemplary embodiment of the present invention provides a method forreceiving a CSI-RS, the method including: receiving a signal througheach of multiple antenna ports; extracting a CSI-RS for each of themultiple antenna ports allocated to a particular Resource Element (RE)from the received signal; demapping a CSI-RS sequence for each antennaport; and acquiring channel state information of each antenna port byusing the demapped CSI-RS sequence, wherein the received signal is asignal generated by allocating CSI-RSs for a total of 8 antenna ports totwo symbols or symbol axes of a time-frequency area within one sub-framein such a manner that CSI-RS allocated REs or sub-carriers adjacent toeach other have an interval of 3 REs or sub-carriers therebetween, and aCSI-RS of a first antenna port and a CSI-RS of a second antenna port arerepeatedly allocated two REs while being discriminated from each otherby orthogonal codes.

An exemplary embodiment of the present invention provides an apparatusto transmit a Channel State Information-Reference Signal (CSI-RS), theapparatus including: a CSI-RS generator for generating a CSI-RS sequencefor an antenna port for transmission of a maximum of N (N being aninteger larger than or equal to 1) number of CSI-RSs; a CSI-RS resourceallocator to map the generated CSI-RS sequence to Resource Elements(REs) allocated for transmission of the CSI-RS; and an OFDM signalgenerator to generate an Orthogonal Frequency Division Multiplexing(OFDM) signal including information on the mapped CSI-RS sequence and totransmit the generated OFDM signal to a reception apparatus, wherein theCSI-RS resource allocator maps the CSI-RS sequence to REs correspondingto one sub-carrier at every 12 sub-carriers with respect to two OFDMsymbols or symbol axes for each antenna port within a particularsub-frame by which the CSI-RS is transmitted, for a total of ┌N/2┐antenna port sets, each of which includes either both an M^(th) (M≤N,and M being an odd number) antenna port and an (M+1)^(th) antenna portor only the M^(th) antenna port when the (M+1)^(th) antenna port doesnot exist and is used as an antenna port set for transmission of oneCSI-RS, a CSI-RS of antenna ports within each of the antenna port setsis allocated to REs having the same time-frequency resource and arediscriminated from each other by orthogonal codes, and the CSI-RSallocated REs of different antenna port sets adjacent to each other inthe frequency axis are spaced apart from each other with an interval of3 REs.

An exemplary embodiment of the present invention provides an apparatusto receive a CSI-RS, the apparatus including: a reception processingunit to receive a transmitted signal; a CSI-RS extraction unit toextract CSI-RS information for each of multiple antenna ports allocatedto a particular Resource Element (RE) through resource element demappingof the received signal; and a channel state measurement unit foracquiring channel state information from the extracted CSI-RSinformation, wherein, in the transmitted signal, for an antenna port fortransmission of a maximum of N (N being an integer larger than or equalto 1) number of CSI-RSs, the CSI-RS sequence is mapped to REscorresponding to one sub-carrier at every 12 sub-carriers with respectto two Orthogonal Frequency Division Multiplexing (OFDM) symbols orsymbol axes for each antenna port within a particular sub-frame by whichthe CSI-RS is transmitted, for a total of ┌N/2┐ antenna port sets, eachof which includes either both an M^(th) (M≤N, and M being an odd number)antenna port and an (M+1)^(th) antenna port or only the M^(th) antennaport if the (M+1)^(th) antenna port does not exist and is used as anantenna port set for transmission of one CSI-RS, a CSI-RS of antennaports within each of the antenna port sets is allocated to REs havingthe same time-frequency resource and are discriminated from each otherby orthogonal codes, and the CSI-RS allocated REs of different antennaport sets adjacent to each other in the frequency axis are spaced apartfrom each other with an interval of 3 REs.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 illustrates a wireless communication system according to anexemplary embodiment of the present invention.

FIGS. 2a to 2c illustrate sub-frame structures of transmission dataaccording to exemplary embodiments of the present invention.

FIG. 3 illustrates examples of mapping of CRSs to a time-frequencyresource block according to an exemplary embodiment.

FIG. 4 is an illustrative view showing a representative example ofmapping a CSI-RS according to an exemplary embodiment.

FIGS. 5 to 7 are illustrative views showing exemplary embodiments ofbasic schemes for CSI-RS allocation for each antenna port according tothe FDM, (FDM+TDM), and (FDM+CDM) schemes, respectively.

FIG. 8 is a block diagram illustrating the configuration of a CSI-RSallocation apparatus to generate a CSI-RS and to allocate the generatedCSI-RS to Resource Elements (REs) according to an exemplary embodimentof the present invention.

FIG. 9 is a block diagram illustrating the structure for signalgeneration of a downlink physical channel in a wireless communicationsystem according to an exemplary embodiment.

FIGS. 10 to 12 are illustrative views showing a scheme for allocatingCSI-RSs according to an exemplary embodiment of the present invention.

FIGS. 13 to 15 are illustrative views showing a scheme for allocatingCSI-RSs according to an exemplary embodiment of the present invention.

FIG. 16 is an illustrative view showing a scheme for allocating CSI-RSsaccording to an exemplary embodiment of the present invention.

FIG. 17 is an illustrative view showing a scheme for allocating CSI-RSsaccording to an exemplary embodiment of the present invention.

FIG. 18 is a block diagram illustrating the configuration of a receiverto receive a CSI-RS according to an exemplary embodiment of the presentinvention.

FIG. 19 is a flowchart illustrating a method of CSI-RS transmissionaccording to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Exemplary embodiments now will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsare shown. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth therein. Rather, these exemplary embodiments areprovided so that this disclosure will be thorough, and will fully conveythe scope of this disclosure to those skilled in the art. Variouschanges, modifications, and equivalents of the systems, apparatuses,and/or methods described herein will likely suggest themselves to thoseof ordinary skill in the art. Same elements, features, and structuresare denoted by same reference numerals throughout the drawings and thedetailed description, and the size and proportions of some elements maybe exaggerated in the drawings for clarity and convenience.

FIG. 1 illustrates a wireless communication system according to anexemplary embodiment of the present invention. Wireless communicationsystems are widely arranged in order to provide various communicationservices, such as voice, packet data, and the like. Referring to FIG. 1,a wireless communication system includes a UE (User Equipment) 10 and aBS (Base Station) 20. As shown in FIG. 1, a plurality of UEs 10 may beincluded in the wireless communication system.

As used herein, the UE 10 may include a user terminal in a wirelesscommunication, a UE in WCDMA, LTE, HSPA (High Speed Packet Access), andthe like, a MS (Mobile Station), a UT (User Terminal), SS (SubscriberStation), a wireless device in GSM (Global System for MobileCommunication), and the like.

The BS 20 may be a cell and may generally refer to a fixed stationcommunicating with the UE 10, and may be a Node-B, eNB (evolved Node-B),BTS (Base Transceiver System), AP (Access Point), relay node, and thelike. That is, as used herein, the BS 20 or cell should be construed ashaving an inclusive meaning indicating an area controlled by a BSC (BaseStation Controller) of the CDMA, a Node B, etc. of the WCDMA, and maycorrespond to one of various coverage areas, which include a mega cell,a macro cell, a micro cell, a pico cell, femto cell, etc.

However, the UE 10 and the BS 20 are not limited to specificallyexpressed terms or words and inclusively indicate two transmitting andreceiving elements used for implementation of the aspects of the presentinvention described herein.

Aspects of the present invention provide for various multiple accessschemes, such as CDMA (Code Division Multiple Access), TDMA (TimeDivision Multiple Access), FDMA (Frequency Division Multiple Access),OFDMA (Orthogonal Frequency Division Multiple Access), OFDM-FDMA,OFDM-TDMA, and OFDM-CDMA, which may be applied to the wirelesscommunication system. However, aspects of the present invention are notlimited thereto.

For an uplink transmission and a downlink transmission, aspects of thepresent invention may provide a TDD (Time Division Duplex) scheme usingdifferent times for transmission or an FDD (Frequency Division Duplex)scheme using different frequencies for transmission.

Exemplary embodiments of the present invention may be applied to aresource allocation in the field of asynchronous wirelesscommunications, which may include the LTE (Long Term Evolution) and theLTE-Advanced (LTE-A) the GSM, the WCDMA, and the HSPA, and in the fieldof synchronous wireless communications, which may include the CDMA,CDMA-2000, and UMB. Aspects of the present invention should not belimited or restrictively construed to a particular wirelesscommunication field, and should be construed to include all technicalfields, to which the aspects of the present invention can be applied.

A wireless communication system, to which aspects of the presentinvention are applicable, can support uplink and/or downlink hybridautomatic repeat request (HARD) and can use a Channel Quality Indicator(CQI) for link adaptation. Further, different multiple access schemesmay be used for downlink transmission and uplink transmission. Forexample, an Orthogonal Frequency Division Multiple Access (OFDMA) schememay be used for the downlink, while a Single Carrier-Frequency DivisionMultiple Access (SC-FDMA) scheme is used for the uplink.

The radio interface protocol layers between a UE and a network can beclassified into the first layer (L1), the second layer (L2), and thethird layer (L3) based on the lower three layers of the Open SystemInterconnection (OSI) model widely known in the communication systems,and the physical layer belonging to the first layer provides aninformation transfer service using a physical channel.

Meanwhile, the wireless communication system according an exemplaryembodiment of the present invention is applied, one radio frame orwireless frame includes ten sub-frames and one sub-frame may include twoslots.

The basic unit for data transmission is a sub-frame, and downlink oruplink scheduling is performed for each sub-frame. One slot may includea plurality of OFDM symbols in the time axis domain (time domain) and aplurality of sub-carriers in the frequency axis domain (frequencydomain).

For example, one sub-frame includes two time slots. Further, in the caseof using a normal Cyclic Prefix (CP) in the time domain, each time slotmay include seven symbols (six or three symbols in the case of using anextended CP), and may include sub-carriers corresponding to a bandwidthof 180 kHz (since one sub-carrier has a bandwidth of 15 kHz, thebandwidth of 180 kHz corresponds to a total of 12 sub-carriers) in thefrequency domain. The time-frequency region, which is defined by oneslot along the time axis and the bandwidth of 180 kHz along thefrequency axis, can be referred to as a Resource Block (RB).

FIG. 2a illustrates a sub-frame structure of transmission data accordingto an exemplary embodiment of the present invention. Referring to FIG.2a , the transmission time of a frame can be divided into multipleTransmission Time Intervals (TTIs) 201, each having a duration of 1.0ms. The terms “TTI” and “sub-frame” have the same meaning, and eachframe has a length of 10 ms and includes 10 TTIs. Further, one TTIincludes two time slots 202 having the same length, wherein each timeslot has a duration of 0.5 ms.

FIG. 2b illustrates a typical structure of one of the time slots 202according to an exemplary embodiment of the present invention. Referringto FIG. 2b , the TTI is a basic transmission unit, and one TTI includesthe two time slots 202 having the same length, wherein each time slothas a duration of 0.5 ms. The time slot includes a plurality of LongBlocks (LBs) 203, each of which corresponds to a symbol. The LBs 203 areseparated from each other by Cyclic Prefixes (CPs) 204. The CPs includea normal CP and an extended CP, which are classified according to thelengths. The multiple LBs within one time slot include seven LBs in thecase of using the normal CPs, while the multiple LBs within one timeslot include six or three LBs in the case of using the extended CPs.

In summary, one TTI or sub-frame 201 may include 14 LB symbols 203 ifthe normal CP 204 is used, and may include 12 LB symbols 203 (6 LBsymbols in a special case) if the extended CP 204 is used. However,aspects of the present invention are not limited to the frame,sub-frame, or time-slot structure as described above.

FIG. 2c illustrates one Resource Block (RB) 230 during one sub-frame orTTI 201 according to an exemplary embodiment of the present invention,wherein each TTI or sub-frame can be divided into 14 symbols (axes) inthe case of normal CP 204 or divided into 12 (or 6) symbols (axes) 203in the case of extended CP 204 in the time domain. Each symbol (axis)can carry one OFDM symbol.

Further, the entire system bandwidth having a length of 20 MHz can bedivided into sub-carriers having different frequencies. For example, asdescribed above, an area, which includes one slot in the time domain andsub-carriers corresponding to the bandwidth of 180 kHz (12 sub-carriersif each sub-carrier has a bandwidth of 15 kHz) in the frequency domain,can be referred to as a Resource Block (RB).

For example, the bandwidth of 10 MHz within one TTI may include 50 RBsin the frequency domain.

In the RB structure shaped like a grid as described above, each unitspace shaped like a grid cell is referred to as a Resource Element (RE).For example, if a resource area includes one sub-frame in the timedomain and sub-carriers corresponding to a bandwidth of 180 kHz in thefrequency domain, and uses normal CPs, wherein each of the sub-carriershas a frequency bandwidth of 15 kHz, the resource area may include atotal of 168 REs (i.e., 14 symbols×12 sub-carriers).

In the LTE communication system, reference signals include aCell-specific Reference Signal (CRS), a Multicast/Broadcast over SingleFrequency Network (MBSFN) reference signal, and a UE-specific referencesignal, and/or Demodulation Reference Signal (DM-RS).

The CRS is included in and transmitted by all downlink sub-frames of acell supporting the Physical Downlink Shared Channel (PDSCH)transmission. Further, the transmission may be performed through one ormultiple antennas, for example, from among antenna Nos. 0 to 3.

Further, one reference signal is transmitted through each downlinkantenna port, and an RE used for transmission of an RS through one portfrom among the antenna ports within a slot cannot be used for anotherantenna port within the same slot.

FIG. 3 illustrates examples of mapping of CRSs to a time-frequencyresource block according to an exemplary embodiment. The examples shownin FIG. 3 include mapping of CRSs to time-frequency REs according tofour different antenna ports. In each antenna port, the REs, to whichCRSs are allocated, have a period of 6 for the sub-carriers.

In FIG. 3, Rp indicates an RE used for transmission of a referencesignal at antenna port p. For example, R₀ indicates an RE used fortransmission of a reference signal at an antenna port 0.

Meanwhile, in the next generation communication technology, the currentCRSs defined for only four existing antennas are insufficient fordetection of channel information at the time of downlink transmission.To this end, a reference signal named “Channel StateInformation-Reference Signal (CSI-RS)” is newly defined in order tosupport a maximum of eight antennas in the downlink, thereby obtainingchannel state information.

According to the current basic definition relating to the CSI-RS,CSI-RSs are mapped to two REs for each antenna port within one radioframe. In other words, CSI-RSs are mapped to two REs for each antennaport in an area including 12 sub-carriers corresponding to one RB alongthe frequency axis and one radio frame corresponding to the time of 10ms including 10 sub-frames along the time axis. That is, for a total ofeight antenna ports, a maximum of 16 REs are allocated to andtransmitted by a sub-frame or sub-frames. At this time, all of the 16REs may be allocated to and transmitted by one sub-frame from among theten sub-frames (in this case, the CSI-RSs are transmitted at a period of10 ms), or may be allocated to and transmitted by two or more sub-framesfrom among the ten sub-frames.

For example, the CSI-RSs may be divided into two groups(sets) eachcorresponding to a maximum of 8 REs and may be then transmitted by twosub-frames from among the ten sub-frames. At this time, the CSI-RSs aretransmitted at a period of 5 ms or 10 ms.

Meanwhile, a communication system using a maximum of 64 (i.e., 8×8)Multiple Input Multiple Output (MIMO) antennas at both the transmissionport and the reception port is being discussed. In the discussedcommunication system, since different CSI-RSs according to the antennaports or antenna layers should be transmitted, a transmitter shouldallocate CSI-RSs for a total of eight antenna ports to a time-frequencydomain in a discriminated manner. Especially, the CSI-RSs may beallocated in a manner capable of discriminating cells from each other inthe multi-cell environment.

According to aspects of the present invention, antenna layers may bedata layers, which can be logically simultaneously transmitted from abase station or a mobile communication terminal to multiple antennaports. However, the antenna layers may have the same data or differentdata. Therefore, the number of the antenna layers may be equal to orsmaller than the number of antenna ports. Meanwhile, an antenna portnumber is used to express each time-frequency resource area. Therefore,among antenna ports used for the same purpose, different antenna portnumbers indicate different antennas corresponding to spatiallydiscriminated time-frequency resource areas.

For example, antenna port numbers for CRSs using a maximum of fourantennas include 0 to 3. Further, in the case of MB SFN-RS, LTE Rel-8UE-specific RS (DM-RS), and PRS (Positioning Reference Signal), each ofwhich uses a maximum of one antenna, antenna port numbers include 4, 5,and 6. Further, in the case of LTE Rel-10 DM-RS, which uses a maximum of8 antennas, antenna port numbers include 7 to 14. In the case of CSI-RS,which also uses a maximum of 8 antennas, numbers following 14 may beused for antenna port numbers. That is, antenna port numbers 15 to 22may be used for antenna port numbers, and antenna port number 15 may beused for the first antenna port for CSI-RS transmission. At this time,within each particular reference signal, different antenna port numbersindicate antennas having spatially discriminated time-resource areas.

The following description is based on an antenna port, although it canbe applied to an antenna layer.

FIG. 4 is an illustrative view showing a representative example ofmapping a CSI-RS according to an exemplary embodiment. Referring to FIG.4, in a case where a normal CP (Cyclic Prefix) of a normal subframe isused for a single subframe, locations of the CRS (Cell-specificReference Signal), the control region, and the LTE Rel-9/10 DM-RS(Demodulation Reference Signal), among a total of 14 symbols are takeninto consideration, and normal CPs can be allocated to the 10th or 11thsymbol and then transmitted while preventing the normal CPs fromoverlapping with the CRS, the control region, and the LTE Rel-9/10DM-RS. However, aspects of the present invention are not limited to thisconfiguration. For reference, a UE-specific RS (or DM-RS) region of theLTE Rel-8 is not shown in FIG. 4.

At this time, if CSI-RSs are allocated to 16 REs in a single subframe,REs may be transmitted in such a manner that each of 2 symbols (orsymbol axes) includes 8 REs. If CSI-RSs corresponding to 8 REs areallocated to a single subframe, REs may be transmitted in such a mannerthat the 8 REs are all allocated to a single symbol (or symbol axis).The REs may be transmitted in such a manner that each of 2 symbols (orsymbol axes) includes 4 REs.

FIGS. 5 to 7 are illustrative views showing exemplary embodiments ofbasic schemes for CSI-RS allocation for each antenna port according tothe FDM, (FDM+TDM), and (FDM+CDM) schemes, respectively.

In FIGS. 5 to 7, an RE indicated by a reference numeral represents an REallocated to a CSI-RS, and the reference numeral represents a number ofan antenna port allocated to a CSI-RS. In this case, the antenna portnumber signifies a number of an antenna port for transmitting a CSI-RS.The antenna port numbers may be obtained by sequentially numbering, butnot necessarily consecutively numbering, for example, “1” to “8” inconsideration of a maximum of 8 CSI-RS transmission antennas. Also, theantenna port numbers do not signify reference numerals indicatingabsolute antenna port numbers considering all RSs.

In an FDM scheme as shown in FIG. 5, 8 antenna ports are distinguishedonly by frequency resources. A single Resource Block (RB) includes 12subcarriers along the frequency axis. Therefore, if 8 subcarriers aredistinguished within a single symbol axis as shown in the FDM scheme ofFIG. 5, the 8 subcarriers can be used to distinguish between all 8antenna ports. Herein, CSI-RS allocation overhead is 2 REs per antennaport (i.e., 16 REs for the 8 antenna ports) in a region of subcarriers,the number of which is 10 ms (140 symbols for a normal subframe havingnormal CPs)×12 as described above. Therefore, 8 REs can be allocated toeach of 2 subframes.

In an (FDM+TDM) scheme as illustrated in FIG. 6, 8 antenna ports aredistinguished by frequency and time resources. In the (FDM+TDM) scheme,4 antennas are distinguished by the frequency axis, and 4 antenna portsare again distinguished by different symbols along the time axis. As aresult, a total of 8 antenna ports can be distinguished.

In an (FDM+CDM) scheme as illustrated in FIG. 7, 8 antenna ports aredistinguished by frequency and code resources. In the (FDM+CDM) scheme,4 antenna ports are distinguished by the frequency axis, and 4 antennaports are again distinguished by different codes. As a result, a totalof 8 antenna ports can be distinguished. For example, No. 1 antenna andNo. 2 antenna are allocated to the same RE and the same RE allocated theNo. 1 antenna and No. 2 antenna is then transmitted in a time-frequencydomain. However, the No. 1 antenna and No. 2 antenna are distinguishedby different codes, such as the Orthogonal Cover Code (OCC), which havethe orthogonality.

FIGS. 5 to 7 illustrate basic schemes for CSI-RS allocation for eachantenna port according to the FDM, (FDM+TDM), and (FDM+CDM) schemes,respectively. However, aspects are not limited thereto such that variousmethods may be provided according to CSI-RS allocation overhead andschemes equivalent to the schemes as described above.

Moreover, the schemes for CSI-RS pattern allocation as illustrated inFIG. 4 and FIGS. 5 to 7 all have perfect orthogonality for each antennaport, and are distinguished from one another. However, if the schemesfor the CSI-RS pattern allocation as described above are used and BaseStations (BSs) or cells are distinguished only by CSI-RS sequencesmapped to defined CSI-RS patterns respectively, many neighboring cellsmay simultaneously transmit CSI-RSs through the same time-frequencyresource. As a result, there may exist a problem in that interferencebetween neighboring cells causes performance degradation.

Particularly, in a communication system such as a Cooperative MultipointTx/Rx System (CoMP), in which the relevant user needs totransmit/receive a reference signal to/from a neighboring cell as wellas a serving cell, which currently performs main transmission/reception,reception power of a CSI-RS of the neighboring cell is weaker than thatof the serving cell. Therefore, if the serving cell and the neighboringcell simultaneously transmit CSI-RSs through the same time-frequencyresource, the relevant user has difficulty in properly detecting theCSI-RS from the neighboring cell.

Accordingly, aspects of the present invention provide a scheme, in whicha CSI-RS is allocated (or mapped) and the allocated (or mapped) CSI-RSis then transmitted in such a manner that each cell may haveorthogonality (in the CoMP) or quasi-orthogonality (in a non-CoMP) withrespect to time-frequency resources, and thereby it is possible toreduce performance degradation caused by interference betweenneighboring cells.

FIG. 8 is a block diagram illustrating the configuration of a CSI-RSallocation apparatus to generate a CSI-RS and to allocate the generatedCSI-RS to Resource Elements (REs) according to an exemplary embodimentof the present invention. Referring to FIG. 8, a CSI-RS allocationapparatus 800 according to an exemplary embodiment includes a CSI-RSgenerator 810 and a CSI-RS resource allocator 820.

The CSI-RS generator 810 receives external information, such assystem-specific information, and generates a CSI-RS or a CSI-RS sequencebased on the received external information. At this time, thesystem-specific information may include at least one of BS information(e.g., cell IDs), relay node information, UE information, subframenumbers, slot numbers, OFDM symbol numbers, and CP sizes. However,aspects of the system-specific information are not limited to thisconfiguration. Meanwhile, the BS (or cell) information, for example, maybe BS antenna information, BS bandwidth information, and/or BS cell IDinformation.

For example, the CSI-RS generator 810 determines a length of a sequenceby using system-specific information, such as antenna or bandwidthinformation of a BS, and receives cell ID information and selects aCSI-RS of the relevant cell ID, which has been previously determined.

The CSI-RS resource allocator 820 receives the system-specificinformation and frame timing information, and allocates CSI-RSsaccording to antenna ports, which have been generated by the CSI-RSgenerator 810, to a time-frequency resource region. Thereafter, theCSI-RSs allocated to REs are multiplexed with BS transmission frames.

The CSI-RS resource allocator 820 performs allocates resources of anOFDM symbol (i.e., the x-axis) and a subcarrier location (i.e., they-axis) by predetermined rules in a resource allocation method forCSI-RSs, and multiplexing allocated resources with BS transmissionframes at specific frame timing.

Meanwhile, when allocating a CSI-RS for each of a maximum of 8 antennaports to a time-frequency domain, the CSI-RS resource allocator 820,according to aspects of the present invention, allocates CSI-RSsaccording to antenna ports to 4 REs or subcarriers on a basis of asingle symbol (or symbol axis) in a single subframe or Resource Block(RB). At this time, the CSI-RS resource allocator 820 may allocate theCSI-RSs in such a manner that a distance between neighboring CSI-RSallocation REs or subcarriers may become as long as 3 REs orsubcarriers.

In other words, the CSI-RS resource allocator further includes that; theCSI-RS resource allocator maps the CSI-RS sequence to REs correspondingto one sub-carrier at every 12 sub-carriers for each antenna port withrespect to two OFDM symbols within a sub-frame by which the CSI-RS istransmitted, for ┌N/2┐ antenna port sets, each of which includes eitherboth an M^(th) (M≤N, and M being an odd number) antenna port and an(M+1)^(th) antenna port or only the M^(th) antenna port if the(M+1)^(th) antenna port does not exist and is used as an antenna portset for transmission of the CSI-RS, a CSI-RS of antenna ports withineach of the antenna port sets is allocated to REs having the sametime-frequency resource and are discriminated from each other byorthogonal codes, and the CSI-RS allocated for two adjacent antenna portsets within a resource block are spaced apart from each other with aninterval of 3 REs in the frequency axis.

A more detailed description will be made as follows. When allocating aCSI-RS for each of a maximum of 8 antenna ports to a time-frequencydomain in a first scheme, the CSI-RS resource allocator 820, accordingto aspects of the present invention, allocates CSI-RSs to 2 symbols (orsymbol axes) in a single subframe. At this time, the CSI-RS resourceallocator 820 individually allocates a CSI-RS for each of a total of the8 antenna ports to a single RE in a first subframe. Other than this, theCSI-RS resource allocator 820 distinguishes CSI-RSs according to antennaports excluding the previously-allocated antenna ports from CSI-RSsaccording to the previously-allocated antenna ports by using theOrthogonal Cover Code (OCC), and duplicately allocates each of thedistinguished CSI-RSs according to the antenna ports to 2 REs in a firstsubframe. The first scheme, which has been applied to the firstsubframe, is similarly applied to another or second subframe to which aCSI-RS for each of a total of the 8 antenna ports is to be allocated.The first scheme will be described in further detail referring to FIGS.10 to 12 (individual allocation of a CSI-RS for each of the 8 antennaports to a single RE) and FIG. 16 (duplicate allocation of each pair ofthe distinguished CSI-RSs according to the 8 antenna ports to 2 REs).

When allocating a CSI-RS for each of a maximum of 8 antenna ports to atime-frequency domain in a second scheme, the CSI-RS resource allocator820, according to aspects of the present invention, allocates CSI-RSs to2 symbols (or symbol axes) in a single subframe. At this time, theCSI-RS resource allocator 820 individually allocates a CSI-RS for eachof a total of 4 antenna ports to 2 REs in a first subframe. However, theCSI-RS resource allocator 820 may distinguish CSI-RSs according toantenna ports excluding the previously-allocated antenna ports fromCSI-RSs according to the previously-allocated antenna ports by using theOrthogonal Cover Code (OCC), and may duplicately allocate each of thedistinguished CSI-RSs according to the antenna ports to 4 REs in a firstsubframe. The second scheme, which has been applied to the firstsubframe, is similarly applied to another or second subframe to which aCSI-RS for each of the remaining 4 antenna ports excluding the 4 antennaports allocated to the first subframe is to be allocated. The secondscheme will be described in further detail referring to FIGS. 13 to 15(individual allocation of a CSI-RS for each of the 4 antenna ports to 2REs) and FIG. 17 (duplicate allocation of each pair of the distinguishedCSI-RSs according to the 4 antenna ports to 4 REs).

Also, a CSI-RS for a particular antenna port may be allocated in such amanner as to have frequency shifts in the direction of the frequencyaxis according to cells (or cell groups). Particularly, a CSI-RS for thesame antenna port can be allocated in such a manner as to have shifts ona basis of a single subcarrier or RE in the direction of the frequencyaxis according to 3 cells (or cell groups). Accordingly, the cells (orcell groups) can have perfectly-distinguished CSI-RS allocationpatterns, respectively.

Also, locations of the first and second frames as described above can bedifferently allocated in a radio frame for each cell (or cell group).

Meanwhile, in the first scheme as illustrated in FIGS. 10 to 12 and FIG.16, numbers of antenna ports allocated CSI-RSs may be arranged on thesame symbol (or symbol axis) in such a manner so as to alternate in thedirection of the frequency axis. Also, a CSI-RS for the same antennaport can be allocated in such a manner that a shift between 2 REsrespectively belonging to the first and second subframes, each of whichis allocated a CSI-RS for the same antenna port, may become as long as 6REs or subcarriers. However, aspects are not limited thereto.

An example, in which the CSI-RS allocation apparatus 800 according to anexemplary embodiment is used for a wireless communication system usingOFDM and MIMO, will be described as follows.

FIG. 9 is a block diagram illustrating the structure for signalgeneration of a downlink physical channel in a wireless communicationsystem according to an exemplary embodiment.

Referring to FIG. 9, a wireless communication system 900, according toan exemplary embodiment, includes a resource element mapper 910 and aCSI-RS allocation apparatus 800. The CSI-RS allocation apparatus 800 mayinclude a CSI generator 810 and a CSI-RS resource allocator 820.

Meanwhile, the wireless communication system 900, shown in dotted lines,may further include a scrambler, a modulation mapper, a layer mapper, aprecoder, an OFDM signal generator, etc., which are elements of a basictransmission apparatus in a Base Station (BS). However, aspects of thepresent invention as described above are not limited thereto.

Further, the wireless communication system 900 may be a communicationsystem of the BS 10 as illustrated in FIG. 1.

A basic operation of the wireless communication system 900 will bedescribed as follows. Bits, which go through channel coding and areinput in the form of code words in a downlink, are scrambled by thescrambler, and are then input to the modulation mapper. The modulationmapper modulates the scrambled bits to a complex modulation symbol.Then, the layer mapper maps the complex modulation symbol to a singletransmission layer or multiple transmission layers. Then, the precoderprecodes the complex modulation symbol over each transmission channel ofan antenna port. Thereafter, the resource element mapper maps thecomplex modulation symbol for each antenna port to a relevant resourceelement.

The CSI-RS generator 810 generates a CSI-RS, and provides the generatedCSI-RS to the CSI-RS resource allocator 820. Then, the CSI-RS resourceallocator 820, individually or in connection with the resource elementmapper, allocates CSI-RSs according to antenna ports to a time-frequencydomain in the scheme as described above, and multiplexes the allocatedCSI-RSs with BS transmission frames at a specific timing.

At this time, the CSI-RS resource allocator 820 may first allocate RSs,which include the CSI-RSs according to the antenna ports, and controlsignals to resource elements, and may allocate data received from theprecoder to the remaining resource elements.

Thereafter, the OFDM signal generator generates a complex time domainOFDM signal for each antenna port, and transmits the generated complextime domain OFDM signal through the relevant antenna port.

Although the CSI-RS allocation apparatus 800 and the resource elementmapper 910 are described and shown separately, aspects are not limitedthereto such that the CSI-RS allocation apparatus 800 and the resourceelement mapper 910 may be implemented by integrating them in an aspectof hardware or software according to exemplary embodiments of thepresent invention.

The structure for signal generation of the downlink physical channel inthe wireless communication system, according to aspects of the presentinvention, has been described as above with reference to FIG. 9.However, aspects of the present invention are not limited thereto.Namely, in the structure for signal generation of the downlink physicalchannel in the wireless communication system, according to aspects ofthe present invention, other elements, which are different from theelements as described above, may be omitted, the elements may bereplaced or changed with other elements, or other elements may befurther included.

FIGS. 10 to 12 are illustrative views showing a scheme for allocatingCSI-RSs in a (FDM+TDM) scheme by a CSI-RS allocation apparatus accordingto an exemplary embodiment of the present invention for cells (or cellgroups) A, B, and C, respectively.

When allocating a CSI-RS for each of a maximum of 8 antenna ports to atime-frequency domain in an exemplary embodiment as illustrated in FIG.10, the CSI-RS allocation apparatus can individually allocate a CSI-RSsfor each of 4 antenna ports to a single RE or subcarrier within a firstsymbol (or symbol axis) in a first subframe or resource block.Therefore, a CSI-RS for each of the 4 different antenna ports isallocated to one of 4 REs. Then, the CSI-RS allocation apparatus canindividually allocate a CSI-RS for each of remaining 4 antenna ports,which are not allocated to the first symbol (or symbol axis), to asingle RE within a second symbol (or symbol axis) in the same subframe.

Therefore, CSI-RSs according to different antenna ports are allocated toCSI-RS allocation REs, which are adjacent within the first and secondsymbols (or symbol axes), respectively. A distance between the CSI-RSallocation REs may be as long as 3 REs or carriers in the direction ofthe frequency axis.

Herein, an RE, which is allocated a CSI-RS for a particular antennaport, will be referred to as a “CSI-RS allocation RE.”

Namely, in exemplary embodiments as illustrated in FIGS. 10 to 12, aCSI-RS for each of 4 antenna ports is individually allocated to one of 4REs corresponding to 4 subcarriers among 12 subcarriers along thefrequency axis within a single symbol axis in a single Resource Block(RB). At this time, a distance between a CSI-RS allocation RE allocatedto each antenna port and a neighboring CSI-RS allocation RE may be aslong as 3 subcarriers.

A CSI-RS for each of remaining 4 antenna ports is individually allocatedto another symbol axis in the scheme as described above. In this case, aCSI-RS for each of a total of 8 antenna ports is allocated to a singleRE in a single subframe. The CSI-RSs are allocated to 2 subframes amonga total of 10 subframes in the scheme as described above inconsideration of CSI-RS allocation overhead (such that a CSI-RS for eachantenna port should be allocated to 2 REs in a single radio frame).However, if the CSI-RS allocation overhead is changed, aspects of thepresent invention are not limited thereto. However, a scheme for CSI-RSallocation in a single subframe may be the same even if the CSI-RSallocation overhead is changed.

The CSI-RS mapping or allocation scheme according to aspects of thepresent invention as described above can be defined by equation (1)below. However, equation (1) expresses a representative example forpurposes of understanding, and may be differently expressed whilemaintaining the basic scheme as described above.

$\begin{matrix}{{k = {{12 \cdot m} + {\left( {v + v_{shift}} \right){mod}\; 12}}}{l = \left\{ {{{\begin{matrix}10 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 1},2,3,4} \\9 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 5},6,7,8}\end{matrix}{where}\mspace{14mu} m} = 0},1,2,\ldots\mspace{14mu},{N_{RB}^{DL} - 1},{v = \left\{ {\begin{matrix}0 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 1},{{7\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 1}} \\6 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 2},{{8\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 1}} \\3 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 3},{{5\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 1}} \\9 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 4},{{6\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 1}} \\6 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 1},{{7\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 6}} \\0 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 2},{{8\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 6}} \\9 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 3},{{5\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 6}} \\3 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 4},{{6\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 6}}\end{matrix},{{{and}v_{shift}} = {N_{ID}^{cell}{mod}\; 12.}}} \right.}} \right.}} & (1)\end{matrix}$

Herein, k represents a subcarrier number of an RE allocated a CSI-RS. lof an RE allocated a CSI-RS represents symbol (or symbol axis) numbers 0to 13. └n_(s)/2┘ represents subframe numbers 0 to 9.

└n_(s)/2┘ represents a subframe number, and is described as having avalue of 1 or 6. However, aspects of the present invention are notlimited thereto. └n_(s)/2┘ may indicate 2 optional subframes among 10subframes included in a single radio frame.

Also, equation (1) defines 1 of an RE allocated a CSI-RS to have 9 or 10as a symbol (or symbol axis) number. However, aspects of the presentinvention are not limited thereto. Two optional symbols (or symbolaxes), which are adjacent or not adjacent, may be used among a total of14 symbols or symbol axes if a normal CP is used, and if an extended CPis used, the number of symbols or symbol axes may be 12 or 6.

Also, as in FIG. 10 and equation (1), 4 antenna ports, which areallocated to each of the first and second symbols (or symbol axes)defined as l=9 and 10, are grouped into antenna port numbers 5 to 8 andantenna port numbers 1 to 4. However, aspects of the present inventionare not limited thereto. It is also possible to group the 8 antennaports in other schemes.

Also, if CSI-RS allocation REs for the 4 antenna ports 5 to 8 arearranged within the first symbol (or symbol axis), adoption can be madeof a scheme in which the CSI-RS allocation REs are not arranged in orderbut are alternately arranged one by one. Namely, if a CSI-RS for theantenna port 7 is allocated to an RE located at (l, k)=(9, 0) as in FIG.10 and equation (1), an RE located at (l, k)=(9, 3), which is adjacentalong the frequency axis (i.e., distant by 3 REs), is not allocated theantenna port 6 but a CSI-RS for the antenna port 5, which is the nextantenna port. Then, a CSI-RS for the antenna port 8 may be allocated toan RE located at (l, k)=(9, 6).

CSI-RS allocation REs for neighboring antenna ports are alternatelyarranged one by one in the scheme as described above, and therebyinterference between antenna ports can be reduced. However, aspects ofthe present invention are not limited thereto.

If a single radio frame includes 2 subframes allocated CSI-RSs asdescribed above and the 2 subframes are defined as first and secondsubframes, a shift between CSI-RS allocation REs for a particularantenna port in the first and second subframes may be as long as 6 REsas illustrated in FIG. 10.

Namely, if the antenna port 1 is taken as an example, a CSI-RSallocation RE for the antenna port 1 is located at (l, k)=(10, 0) in thefirst subframe as illustrated in FIG. 10. On the other hand, aCSI-allocation RE for the antenna port 1 is allocated to (l, k)=(10, 6),which is shifted as long as 6 subcarriers or REs in the direction of thefrequency axis, in the second subframe.

Interference between antenna ports can be decreased in the scheme asdescribed above. However, aspects of the present invention are notlimited thereto.

The first and second subframes may be optional in determining thelocations thereof but may have an appropriate distance therebetweenwithin a single radio frame. For example, if numbers of subframesincluded in the radio frame are defined to be 0 to 9 and the firstsubframe is located at the subframe number 1, the second subframe isarranged at the subframe number 6 among the subframe numbers. However,aspects of the present invention are not limited thereto, and the firstand second subframes may be adjacent or arranged differently.

Namely, CSI-RSs are allocated to 2 subframes among a total of 10subframes in consideration of CSI-RS allocation overhead. The 2subframes may be continuous or may have a specific period. Namely, the 2subframes having similar configurations are transmitted in the scheme ofFIG. 10. Therefore, the 2 subframes may be transmitted at intervals of 5ms, which is obtained by dividing a total of 10 ms by 2.

Alternate CSI-RS allocation between cells (or cell groups) will bedescribed referring to FIGS. 11 and 12 based on FIG. 10.

According to FIGS. 11 and 12 and equation (1), a scheme for CSI-RSallocation for each antenna port may be similar to as illustrated inFIG. 10, and a CSI-RS for each antenna port can be allocated in such ascheme as to have offsets or frequency shifts according to cells (orcell groups).

In other words, if multiple resource blocks are included, each antennaport allocates a CSI-RS to each 12^(th) subcarrier and transmits each12^(th) subcarrier allocated the CSI-RS in view of the entire frequencyaxis.

Referring to FIG. 10, the CSI-RS antenna port 1, for example, is mappedto each (k=12·m)^(th) (m=0, 1, 2, . . . , N_(RB) ^(DL)−1) subcarrierwithin the 11^(th) symbol (having a symbol number 10) in a particularsubframe. Herein, N_(RB) ^(DL) is a value obtained by representing adownlink bandwidth on a RB-by-RB basis. Also, a total 12 of 0 to 11offsets or frequency shifts according to cell groups may be expressed byk=12·m+v_(shift) (m=0, 1, 2, . . . , N_(RB) ^(DL)−1).

At this time, there may be different values of v_(shift) according tothe cells (or cell groups). For example, v_(shift) may be expressed byv_(shift)=N_(ID) ^(cell) mod12 according to Physical Cell Identities(PCIs), which are cell IDs.

If the 12 offsets or frequency shifts are also applied to each of otherantenna ports according to PCIs in the above scheme, a distance betweenCSI-RSs allocated for each of antenna ports may be as long as 3subcarriers. Therefore, a total of 3 cell groups (a cell group A: N_(ID)^(cell) mod3=0, a cell group B: N_(ID) ^(cell) mod3=1, and a cell groupC: N_(ID) ^(cell) mod3=2) have perfectly-distinguished CSI-RS allocationpatterns with respect to time-frequency resources, respectively.

If the antenna port 7 is taken as an example, the CSI-RS allocationpatterns signify a scheme in which the antenna port 7 is allocated to(l, k)=(9, 0) (FIG. 10 and N_(ID) ^(cell) mod3=0) in the cell group A,but the antenna port 7 is allocated to (l, k)=(9, 1) (FIG. 11 and N_(ID)^(cell) mod3=1) in the cell group B, and the antenna port 7 is allocatedto (l, k)=(9, 2) (FIG. 12 and N_(ID) ^(cell) mod3=2) in the cell groupC.

Also, the locations of the first and second subframes may be differentlyarranged for each cell group. In other words, in FIGS. 10 to 12, offsetsor frequency shifts according to cell groups may be applied to alocation of CSI-RS allocation in the direction of the frequency axis foreach antenna port in a single subframe, and thereby CSI-RS allocationpatterns may be differently defined among neighboring cells. However,further, subframes allocated CSI-RSs may be made different for eachneighboring cell.

For example, when the 2^(nd) and 7^(th) subframes, which have beenallocated CSI-RSs, among 10 subframes have been transmitted by aparticular cell group, the 3^(rd) and 8^(th) subframes are transmittedby another cell group. By making the relative locations of the first andsecond subframes different for each cell group in this manner,interference between neighboring cells may be further reduced.

Also, a CSI-RS allocation RE for each of 8 antenna ports is arranged inthe first subframe. Therefore, (the number of CSI-RS allocation REs foreach antenna port×the number of antenna ports) can be defined as (1×8)on a subframe-by-subframe basis. There may be a total of 2 subframes,which satisfy the above definition, including the first subframe.Accordingly, (the number of CSI-RS allocation REs for each antennaport×the number of antenna ports) is equal to (2×8) on a radioframe-by-radio frame basis. Hence, a required CSI-RS allocation overheadis satisfied.

In a cooperative multi-antenna transmission/reception system, such as aCoMP, in which a User Equipment (UE) should receive a CSI-RS of a cellother than a serving cell, the UE may perform blanking for leaving datablank without transmitting the data or muting for transmitting data withzero power with respect to REs through which CSI-RSs are transmitted bya cell group other than a cell group, to which the UE and the servingcell belong, among a total of 3 cell groups.

Namely, in FIG. 10, the cell group A does not transmit data or transmitsdata with zero power to REs located at (l, k)=(9 or 10, 1 or 2), throughwhich the cell groups B and C transmit CSI-RSs, so that there may exista perfect orthogonality between cells in the 3 cell groups. Accordingly,interference between neighboring cells may be decreased. Further, thismay be referred to as an orthogonal state for each cell.

However, in this case, CSI-RS allocation overhead increases by leavingthe place blank instead of the existing transmission of data. Then, theincreased CSI-RS allocation overhead reduces a data transmission rate.

Therefore, in a non-CoMP communication system in which a UE does notneed to receive a CSI-RS of a cell other than a serving cell, in ordernot to cause the increase of CSI-RS allocation overhead, the UEconsiders interference to some degree, which is caused by data, and maytransmit data to REs through which CSI-RSs are transmitted by a cellgroup other than a cell group, to which the UE and the serving cellbelong, among a total of 3 cell groups. This can be referred to as aquasi-orthogonal state for each cell.

However, even though there exists the quasi-orthogonality between cellsin the 3 cell groups, cell groups corresponding to neighboring cells donot simultaneously transmit CSI-RSs through the same time-frequencyresource. Therefore, it is possible to reduce performance degradationcaused by interference between the neighboring cells.

FIGS. 13 to 15 are illustrative views showing a scheme for CSI-RSallocation in (FDM+TDM) according to an exemplary embodiment of thepresent invention for cells (or cell groups) A, B, and C, respectively.

When a CSI-RS for each of a maximum of 8 antenna ports is allocated to atime-frequency domain in an exemplary embodiment of FIGS. 13 to 15, aCSI-RS for each of 2 antenna ports is individually allocated to 2 REs orsubcarriers within a first symbol (or symbol axis) in a first subframeor Resource Block (RB). A CSI-RS for each of 2 antenna ports excludingthe 2 antenna ports allocated to the first symbol (or symbol axis) isindividually allocated to 2 REs within a second symbol (or symbol axis)in the same subframe. A CSI-RS for each of remaining 4 antenna ports maybe allocated in another second subframe or RB in the scheme as describedabove.

Accordingly, each of the first and second symbols (or symbol axes) isallocated according to (the number of CSI-RS allocation REs for eachantenna port×the number of antenna ports)=(2×2). A distance betweenCSI-RS allocation REs may be as long as 3 REs or subcarriers in thedirection of the frequency axis as described with respect to FIGS. 10 to12.

In other words, in an exemplary embodiment as shown in FIGS. 13 to 15, aCSI-RS for each of 2 antenna ports is individually allocated to 2 REsamong 4 REs corresponding to 4 subcarriers within 12 subcarriers alongthe frequency axis within a single symbol axis in a single RB. At thistime, a distance between CSI-RSs allocated according to antenna portsmay be as long as 3 subcarriers.

A CSI-RS for each of 2 antenna ports excluding 2 allocated antenna portsmay be individually allocated to 2 REs within another symbol axis in thescheme as described above. In this case, a CSI-RS for each of a total ofthe 4 antenna ports is individually allocated to 2 REs in a singlesubframe. A CSI-RS for each of remaining 4 antenna ports excluding 4allocated antenna ports is allocated to 2 REs in another subframe in thescheme as described above. As a result, a CSI-RS for each antenna portmay be individually allocated to 2REs in a total of 10 subframes.

The CSI-RS mapping or allocation scheme according to aspects of thepresent invention as described above can be defined by equation (2)below. However, equation (2) expresses a representative example forpurposes of understanding, and may be differently expressed whilemaintaining the basic scheme as described above.

Subframe A: transmission through CSI-RS antenna ports=1, 2, 3, 4

Subframe B: transmission through CSI-RS antenna ports=5, 6, 7, 8

$\begin{matrix}{{k = {{6 \cdot m} + {\left( {v + v_{shift}} \right){mod}\; 12}}}{l = \left\{ {{{\begin{matrix}10 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 1},2,5,6} \\9 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 3},4,7,8}\end{matrix}{where}\mspace{14mu} m} = 0},1,2,\ldots\mspace{14mu},{{2 \cdot N_{RB}^{DL}} - 1},{v = \left\{ {\begin{matrix}0 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{port}} = 1},4,5,8} \\3 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{port}} = 2},3,6,7}\end{matrix},{{{and}v_{shift}} = {N_{ID}^{cell}{mod}\; 6.}}} \right.}} \right.}} & (2)\end{matrix}$

Herein, k represents a subcarrier number of an RE allocated a CSI-RS. lof an RE allocated a CSI-RS represents symbol (or symbol axis) numbers 0to 13.

Also, equation (2) defines l of an RE allocated a CSI-RS to have 9 or 10as a symbol (or symbol axis) number. However, aspects of the presentinvention are not limited thereto. Two optional symbols (or symbolaxes), which are adjacent or not adjacent, may be used among a total of14 symbols or symbol axes if a normal CP is used, and if an extended CPis used, the number of symbols or symbol axes may be 12 or 6.

Also, as in FIGS. 13 to 15 and equation (2), 4 antenna ports, which areallocated to the first symbol (or symbol axis) defined as l=9, aregrouped into antenna port numbers 3 and 4 in a first subframe, and aregrouped into antenna port numbers 7 and 8 in a second subframe. Fourantenna ports, which are allocated to the second symbol (or symbol axis)defined as l=10, are grouped into antenna port numbers 1 and 2 in afirst subframe, and are grouped into antenna port numbers 5 and 6 in asecond subframe. However, this is just one example, and aspects of thepresent invention are not limited thereto. It is also possible to groupthe 8 antenna ports in other schemes.

Also, when CSI-RS allocation REs for the 2 antenna ports 3 and 4 arearranged within the first symbol (or symbol axis) in the first subframe,adoption can be made of a scheme in which the CSI-RS allocation REs arealternately allocated with each other. Namely, when a CSI-RS for theantenna port 4 is allocated to an RE located at (l, k)=(9, 0) as in FIG.13 and equation (2), a CSI-RS for the antenna port 3 is allocated to anRE located at (l, k)=(9, 3) which is adjacent along the frequency axis(i.e., distant by 3 REs). Then, a CSI-RS for the antenna port 4 isallocated to an RE located at (l, k)=(9, 6). Namely, a distance betweenCSI-RS allocation REs according to antenna ports may be as long as 6 REson the symbol (or symbol axis).

CSI-RS allocation REs for neighboring antenna ports are alternatelyarranged one by one in the scheme as described above, and therebyinterference between antenna ports can be reduced. However, aspects ofthe present invention are not limited thereto.

The first and second subframes may be optional in determining thelocations thereof but may have an appropriate distance therebetween in asingle radio frame. For example, if numbers of subframes included in theradio frame are defined to be 0 to 9 and the first subframe is locatedat the subframe number 1, the second subframe may be arranged at 6 amongthe subframe numbers. However, aspects of the present invention are notlimited thereto, and the first and second subframes may be just adjacentor arranged differently.

According to an exemplary embodiment as illustrated in FIGS. 13 to 15,(the number of CSI-RS allocation REs for each antenna port×the number ofantenna ports) is defined as (2×4) in each of the first and secondsubframes. Accordingly, (the number of CSI-RS allocation REs for eachantenna port×the number of antenna ports) is equal to (2×8) on a radioframe-by-radio frame basis. In this regard, a required CSI-RS allocationoverhead is satisfied.

CSI-RSs are allocated to 2 subframes among a total of 10 subframes inconsideration of CSI-RS allocation overhead. The 2 subframes may becontinuous or may all have a specific period. Namely, the 2 subframeshaving different configurations, in each of which CSI-RSs according tothe 4 antenna ports are allocated, are transmitted in the scheme asillustrated in FIGS. 13 to 15. Therefore, the 2 subframes as continuoussubframes may be transmitted by periods of 10 ms.

Alternate CSI-RS allocation between cells (or cell groups) will bedescribed referring to FIGS. 14 and 15 based on FIG. 13.

According to FIGS. 14 and 15 and equation (2), a scheme for CSI-RSallocation for each antenna port may be similar to as illustrated inFIG. 13, and a CSI-RS for each antenna port can be allocated in such ascheme as to have offsets or frequency shifts according to cells (orcell groups).

In other words, if at least one resource block is included, each antennaport allocates a CSI-RS to each 6^(th) subcarrier and transmits each6^(th) subcarrier allocated to the CSI-RS in view of the entirefrequency axis. Referring to FIGS. 13 to 15, the CSI-RS antenna port 1,for example, is mapped to each (k=6·m)^(th) (m=0, 1, 2, . . . , 2·N_(RB)^(DL)−1) subcarrier or RE within the 11^(th) symbol (having a symbolnumber l=10) in a particular subframe. Herein, a total 6 of 0 to 5offsets or frequency shifts according to cell groups may be expressed byk=6·m+v_(shift) (m=0, 1, 2, . . . , 2·N_(RB) ^(DL)−1). At this time,there may be different values of v_(shift) according to the cells. Forexample, v_(shift) may be expressed by v_(shift)=N_(ID) ^(cell) mod 6according to Physical Cell Identities (PCIs), which are cell IDs.

If the 6 offsets or frequency shifts are also applied to each of otherantenna ports according to PCIs in the above scheme, a distance betweenCSI-RSs allocated for each of antenna ports may be as long as 3subcarriers. Therefore a total of 3 cell groups (a cell group A of FIG.13: N_(ID) ^(cell) mod3=0, a cell group B of FIG. 14: N_(ID) ^(cell)mod3=1, and a cell group C of FIG. 15: N_(ID) ^(cell) mod3=2) haveperfectly-distinguished CSI-RS allocation patterns with respect totime-frequency resources, respectively.

If an example of the antenna port 4 is described in detail referring toFIGS. 13 to 15, the CSI-RS allocation patterns signify a scheme in whichthe antenna port 4 is allocated to (l, k)=(9, 0) (FIG. 13 and N_(ID)^(cell) mod3=0) in the cell group A, but the antenna port 4 is allocatedto (l, k)=(9, 1) (FIG. 14 and N_(ID) ^(cell) mod3=1) in the cell groupB, and the antenna port 4 is allocated to (l, k)=(9, 2) (FIG. 15 andN_(ID) ^(cell) mod3=2) in the cell group C.

Also, the locations of the first and second subframes may be differentlyarranged for each cell group.

In other words, in FIGS. 13 to 15, offsets or frequency shifts accordingto cell groups are applied to a location of CSI-RS allocation in thedirection of the frequency axis for each antenna port in a singlesubframe, and thereby CSI-RS allocation patterns are differently definedamong neighboring cells. However, subframes allocated CSI-RSs may beadditionally made different for each neighboring cell.

For example, when the 2^(nd) and 7^(th) subframes, which have beenallocated CSI-RSs, among 10 subframes have been transmitted by aparticular cell group, the 3^(rd) and 8^(th) subframes are transmittedby another cell group. By making the relative locations of the first andsecond subframes different for each cell group in this manner,interference between neighboring cells may be further reduced. Howeveraspects of the present invention are not limited thereto.

In an exemplary embodiment as illustrated in FIGS. 13 to 15, (the numberof CSI-RS allocation REs for each antenna port×the number of antennaports) is defined as (2×2) on a symbol-by-symbol basis in a singlesubframe. In each of the first and second subframes, (the number ofCSI-RS allocation REs for each antenna port×the number of antenna ports)is defined as (2×4). Accordingly, (the number of CSI-RS allocation REsfor each antenna port×the number of antenna ports) is equal to (2×8) ona radio frame-by-radio frame basis. Hence, a required CSI-RS allocationoverhead is satisfied.

Also, a communication system, such as a CoMP, enables blanking or mutingto be performed in an exemplary embodiment of FIGS. 13 to 15, similar todescribed with respect to FIGS. 10 to 12.

Namely, in a cooperative multi-antenna transmission/reception system,such as a CoMP, in which a User Equipment (UE) may receive a CSI-RS of acell other than a serving cell, the UE may perform blanking for leavingdata blank without transmitting the data or muting for transmitting datawith zero power with respect to REs through which CSI-RSs aretransmitted by a cell group other than a cell group, to which the UE andthe serving cell belong, among a total of 3 cell groups.

Namely, in FIG. 13, the cell group A does not transmit data or transmitsdata with zero power to REs located at (l, k)=(9 or 10, 1 or 2), throughwhich the cell groups B and C transmit CSI-RSs, so that there may exista perfect orthogonality between cells in the 3 cell groups. Accordingly,it is possible to decrease interference between neighboring cells. Thiscan be referred to as an orthogonal state for each cell.

Meanwhile, in a communication system such, as a non-CoMP, in which a UEdoes not need to receive a CSI-RS of a cell other than a serving cell,in order not to cause the increase of CSI-RS allocation overhead, the UEconsiders interference to some degree, which is caused by data, and maytransmit data to REs through which CSI-RSs are transmitted by a cellgroup other than a cell group, to which the UE and the serving cellbelong, among a total of 3 cell groups. This can be referred to as aquasi-orthogonal state for each cell. However, even though there existsthe quasi-orthogonality between cells in the 3 cell groups, cell groupscorresponding to neighboring cells do not simultaneously transmitCSI-RSs through the same time-frequency resource. Therefore, it ispossible to reduce performance degradation caused by interferencebetween the neighboring cells.

In other words, an exemplary embodiment discloses transmitting CSI-RS,wherein the transmitting CSI-RS includes steps of generating CSI-RSsequence for N antenna ports, mapping the generated CSI-RS sequence topredetermined Resource Elements (REs); and transmitting a signalincluding the mapped CSI-RS sequence. Herein, the mapping the generatedCSI-RS sequence to the REs further includes; grouping the N antennaports into at least one antenna port set, and allocating that each ofthe at least one antenna port set includes a pair of two antenna ports,two antenna ports in the same antenna port set are allocated toidentical REs of a time-frequency domain configured by symbols andsub-carriers, in a sub-carrier having an offset determined by a cellamong 12 sub-carriers and consecutive two symbols within one sub-frame,the two antenna ports in the same antenna port set are discriminatedfrom each other by Orthogonal Cover Codes (OCCs), and an intervalbetween antenna sets are spaced by 3 in a frequency domain. And themapping the generated CSI-RS sequence to the REs further includes;allocating that the generated CSI-RS sequence is allocated to REs from asub-carrier having different offset by determined according to the Nantenna ports, in 12 sub-carriers and two symbols and the consecutivetwo symbols within the one sub-frame.

Also, an exemplary embodiment discloses receiving CSI-RS, wherein thereceiving CSI-RS includes steps of receiving a signal; extracting CSI-RSsequence for N antenna ports in predetermined Resource Elements (REs) ofa time-frequency domain configured by symbols and sub-carriers, in asub-carrier having an offset determined by a cell among 12 sub-carriersand consecutive two symbols within one sub-frame from the signal;acquiring channel state information by the extracted CSI-RS sequence.Herein, the extracting CSI-RS sequence further includes; determining atleast one antenna port set of the N antenna ports, and determining thatan interval between antenna port sets are spaced by 3 in a frequencydomain, each of the at least one antenna port set includes a pair of twoantenna ports, and two antenna ports in the same antenna port set arediscriminated from each other by Orthogonal Cover Codes (OCCs) inidentical REs among the predetermined REs. And the extracting of theCSI-RS sequence further includes; determining that the generated CSI-RSsequence is allocated to REs from a sub-carrier having different offsetby determined according to the N antenna ports, in 12 sub-carriers andtwo symbols and the consecutive two symbols within the one sub-frame.

FIG. 16 is an illustrative view showing an exemplary embodiment of ascheme for CSI-RS allocation in (FDM+CDM). When a CSI-RS for each of amaximum of 8 antenna ports allocated to a time-frequency domainaccording to aspects of the present invention as shown in FIG. 16, aCSI-RS for each of the 4 antenna ports is individually allocated to asingle RE or subcarrier within a first symbol (or symbol axis) in afirst subframe or Resource Block (RB). Therefore, each of the 4 REs isallocated a CSI-RS of one of the 4 different antenna ports. Then, eachof the CSI-RSs according to the 4 antenna ports, which have beenallocated to the first symbol (or symbol axis), is equally allocated toa single RE within a second symbol (or symbol axis) in the samesubframe. Consequently, a total of the 8 CSI-RS allocation REs arearranged in the first subframe or RB. Further, CSI-RSs according to theremaining 4 antenna ports are distinguished from the CSI-RSs accordingto the previously-allocated 4 antenna ports by the Orthogonal Cover Code(OCC) in the first subframe or RB. Then, each of the distinguishedCSI-RSs according to the remaining 4 antenna ports can be duplicatelyallocated to 2 CSI-RS allocation REs of the 8 CSI-RS allocation REs inthe first subframe or RB.

Namely, a CSI-RS for each of the 4 antenna ports is allocated to one ofthe 4 REs corresponding to 4 subcarriers among 12 subcarriers along thefrequency axis within the first symbol in a single RB. At this time, adistance between the CSI-RSs allocated according to the 4 antenna portsmay be as long as 3 subcarriers. In the same scheme as described above,a CSI-RS for each of the 4 equal antenna ports is allocated to one ofthe 4 REs within the second symbol (or symbol axis) in the same RB. Inthis case, a CSI-RS for each of a total of the 4 antenna ports isduplicately allocated to the 2 symbols in a single subframe. CSI-RSsaccording to the remaining 4 antenna ports are distinguished from theCSI-RSs according to the previously-allocated 4 antenna ports bydifferent codes, such as the OCC, which have orthogonality, in the samesubframe. For example, the CSI-RS antenna ports 1 and 2 are mapped tothe same RE in the same subframe, and the same RE, which is allocatedthe CSI-RSs according to the CSI-RS antenna ports 1 and 2, istransmitted. If the CSI-RSs according to the CSI-RS antenna ports 1 and2 are allocated to the same RE, the CSI-RSs are distinguished by theOCC. The scheme as described above is similarly applied to the antennaports 3 and 4, 5 and 6, and 7 and 8. The CSI-RSs are allocated to the 2subframes among a total of 10 subframes according to this scheme inconsideration of CSI-RS allocation overhead. However, if the CSI-RSallocation overhead is changed, aspects of the present invention are notlimited thereto. However, according to aspects of the present invention,a scheme for CSI-RS allocation in a single subframe may be the same evenwhen the CSI-RS allocation overhead is changed.

Referring to FIG. 16, the above allocation scheme will be described indetail as follows. CSI-RSs according to the antenna ports 1 and 2distinguished by the OCC are duplicately allocated to 2 REs located at(l, k)=(9 and 10, 0) in the first subframe. CSI-RSs according to theantenna ports 5 and 6 distinguished by the OCC are duplicately allocatedto 2 REs located at (l, k)=(9 and 10, 3) which is as distant as 3 REsfrom the location (9 and 10, 0) in the direction of the frequency axis.

Also, in order to satisfy the requirements of CSI-RS allocationoverhead, CSI-RSs may be allocated even to another or second subframe inthe scheme applied to the first subframe.

At this time, there may be changes in numbers of antenna ports of whichCSI-RSs are duplicately allocated to the same RE, the order of antennaport numbers in the direction of the frequency axis, etc. However, thisis not essential, and aspects of the present invention are not limitedthereto.

The CSI-RS mapping or allocation scheme according to aspects of thepresent invention as described above can be defined by equation (3)below. However, equation (3) expresses a representative example forpurposes of understanding of this embodiment, and may be differentlyexpressed while maintaining the basic scheme as described above.

CSI-RS antenna ports=1, 3, 5, 7: OCC [+1, +1]

CSI-RS antenna ports=2, 4, 6, 8: OCC [+1, −1]

$\begin{matrix}{{k = {{12 \cdot m} + {\left( {v + v_{shift}} \right){{mod}12}}}}{{l = 9},10}{{m = 0},1,2,\ldots\mspace{14mu},{N_{RB}^{DL} - 1}}{v = \left\{ {{\begin{matrix}0 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 1},{{2\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 1}} \\6 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 3},{{4\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 1}} \\3 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 5},{{6\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 1}} \\9 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 7},{{8\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 1}} \\6 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 1},{{2\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 6}} \\0 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 3},{{4\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 6}} \\9 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 5},{{6\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 6}} \\3 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 7},{{8\mspace{14mu}{and}\mspace{14mu}\left\lfloor {n_{s}/2} \right\rfloor} = 6}}\end{matrix}v_{shift}} = {N_{ID}^{cell}{mod}\; 12}} \right.}} & (3)\end{matrix}$

Herein, k represents a subcarrier number of an RE allocated a CSI-RS. lof an RE allocated a CSI-RS represents symbol (or symbol axis) numbers 0to 13. └n_(s)/2┘ represents subframe numbers 0 to 9.

Herein, └n_(s)/2┘ represents a subframe number, and is described ashaving a value of 1 or 6. However, aspects of the present invention arenot limited thereto. └n_(s)/2┘ may indicate 2 optional subframes among10 subframes included in a single radio frame.

Also, equation (3) defines 1 of an RE allocated a CSI-RS to have 9 or 10as a symbol (or symbol axis) number. However, aspects of the presentinvention are not limited thereto. Two optional symbols (or symbolaxes), which are adjacent or not adjacent, may be used among a total of14 symbols or symbol axes if a normal CP is used, and if an extended CPis used, the number of symbols or symbol axes may be 12 or 6.

Further, as described above, numbers of antenna ports of which CSI-RSsare duplicately allocated to the same RE, the order of antenna portnumbers in the direction of the frequency axis, etc. may be changed.Aspects of the present invention are not limited to the example of FIG.16. Namely, in FIG. 16 and equation (3), the antenna ports, which areallocated to the CSI-RS allocation REs in the first subframe, areindicated by (1, 2), (5, 6), (3, 4) and (7, 8) in the order of lowersubcarriers. However, aspects of the present invention are not limitedthereto.

Here, the Orthogonal Cover Code (OCC) may be an optional code systemsuch as the 2-digit Walsh code system, in which codes have mutualorthogonality. Namely, in FIG. 16, a CSI-RS of an antenna port forwardindicated within each RE, for example, is distinguished by an OCC 1,such as [1, 1], and a CSI-RS of an antenna port backward indicatedwithin each RE, for example, is distinguished by an OCC 2, such as [1,−1], which is orthogonal to the OCC 1.

As illustrated in FIG. 16, the 2 antenna ports duplicately allocated to2 REs may be neighboring antenna ports. Namely, in FIG. 16, the 2antenna ports, which are duplicately allocated to (l, k)=(9 and 10, 0),are neighboring antenna ports 1 and 2.

At this time, if a set of 2 antenna ports, which are distinguished bythe OCC and are duplicately allocated to 2 REs, referred to as an“antenna port set,” the order of antenna port sets may be alternatelyallocated in the direction of the frequency axis. However, aspects ofthe present invention are not limited thereto. For example, if anantenna port set (1, 2) is allocated to 2 REs located at k=0 in FIG. 16,2 REs located at k=3, which is next to k=0, are allocated not aneighboring antenna set (3, 4) but an antenna port set (5, 6) which isnext to the antenna set (3, 4). Then, the antenna port set (3, 4) isallocated to 2 REs located at k=6.

The CSI-RS allocation REs for the neighboring antenna port sets may bealternately arranged one-by-one in the scheme as described above, andthereby interference between the neighboring antenna port sets can bereduced. However, aspects of the present invention are not limitedthereto.

Also, in FIG. 16, there may be a difference between the first subframe(shown on the left) and the second subframe (shown on the right) in theorder of antenna port sets in the direction of the frequency axis.However, aspects of the present invention are not limited thereto. Forexample, if the antenna port set (1, 2) is allocated to the 2 REslocated at k=0 in the first subframe as illustrated in FIG. 16, theantenna port set (1, 2) may be allocated to 2 REs located not at k=0 butat k=6 in the second subframe.

The scheme as described above can decrease the interference between theantenna ports. However aspects of the present invention are not limitedthereto.

The first and second subframes may be optional in determining thelocations thereof but may have an appropriate distance there between ina single radio frame. For example, when numbers of subframes included inthe radio frame are defined to be 0 to 9 and the first subframe islocated at the subframe number 1, the second subframe is arranged at 6among the subframe numbers. However, aspects of the present inventionare not limited thereto, and the first and second subframes may be justadjacent.

Namely, CSI-RSs are allocated to 2 subframes among a total of 10subframes in consideration of CSI-RS allocation overhead. The 2subframes may be continuous or may have a specific period. Namely, the 2subframes having similar configurations are transmitted in the scheme ofFIG. 16. Therefore, the 2 subframes may be transmitted at intervals of 5ms, which is obtained by dividing a total of 10 ms by 2.

Alternate CSI-RS allocation between cells (or cell groups) will bedescribed referring to FIGS. 14 and 15 based on FIG. 13.

A scheme for alternate CSI-RS allocation between cells (or cell groups)can also be adopted in an exemplary embodiment of FIG. 16 similar to asin FIGS. 10 to 12.

Namely, according to equation (3), a scheme for CSI-RS allocation foreach antenna port may be similar to as illustrated in FIG. 16, and aCSI-RS for each antenna port may be allocated in such a scheme as tohave offsets or frequency shifts according to cells (or cell groups),even though such scheme is not shown in FIG. 16.

In other words, if at least one resource block is included, each antennaport allocates a CSI-RS to each 12^(th) subcarrier and transmits each12^(th) subcarrier allocated the CSI-RS in view of the entire frequencyaxis. Referring to FIG. 16, the CSI-RS antenna port 1, for example, ismapped to each (k=12·m)^(th) (m=0, 1, 2, . . . , N_(RB) ^(DL)−1)subcarrier within the 10^(th) and 11^(th) symbols (having symbol numbers9 and 10) in a particular subframe. Herein, N_(RB) ^(DL) is a valueobtained by representing a downlink bandwidth on a RB-by-RB basis.Herein, a total 12 of 0 to 11 offsets or frequency shifts according tocell groups may be expressed by k=12·m+v_(shift) (m=0, 1, 2, . . . , 1).At this time, there may be different values of v_(shift) according tothe cells. For example, v_(shift) may be expressed by v_(shift)=N_(ID)^(cell) mod 12 according to Physical Cell Identities (PCIs), which arecell IDs.

If the 12 offsets or frequency shifts are also applied to each of otherantenna ports according to PCIs in the above scheme, a distance betweenCSI-RSs allocated for each of antenna ports may be as long as 3subcarriers. Therefore, a total of 3 cell groups (a cell group A: N_(ID)^(cell) mod3=0, a cell group B: N_(ID) ^(cell) mod3=1, and a cell groupC: N_(ID) ^(cell) mod3=2) have perfectly-distinguished CSI-RS allocationpatterns with respect to time-frequency resources, respectively.

Namely, if the antenna port set (1, 2) is taken as an example, theCSI-RS allocation patterns signify a scheme in which the antenna portset (1, 2) is allocated to (l, k)=(9and 10, 0) (shown on the left inFIG. 16 and N_(ID) ^(cell) mod3=0) in the first subframe and to (l,k)=(9 and 10, 6) (shown on the right in FIG. 16 and N_(ID) ^(cell)mod3=0) in the second subframe in the cell group A, but the antenna portset (1, 2) is allocated to (l, k)=(9 and 10, 1) (N_(ID) ^(cell) mod3=1)in the first subframe and to (l, k)=(9 and 10, 7) (N_(ID) ^(cell)mod3=1) in the second subframe in the cell group B (not shown), and theantenna port set (1, 2) is allocated to (l, k)=(9and 10, 2) (N_(ID)^(cell) mod3=2) in the first subframe and to (l, k)=(9 and 10, 8)(N_(ID) ^(cell) mod3=2) in the second subframe in the cell group C (notshown).

Also, the locations of the first and second subframes may be differentlyarranged for each cell group.

In other words, according to aspects of the present invention, offsetsor frequency shifts according to cell groups are applied to a locationof CSI-RS allocation in the direction of the frequency axis for eachantenna port in a single subframe, and thereby CSI-RS allocationpatterns are differently defined among neighboring cells. However,further, subframes allocated CSI-RSs may be made different for eachneighboring cell.

For example, when the 2^(nd) and 7^(th) subframes, which have beenallocated CSI-RSs, among 10 subframes have been transmitted by aparticular cell group, the 3^(rd) and 8^(th) subframes are transmittedby another cell group. By making the relative locations of the first andsecond subframes different for each cell group in this manner,interference between neighboring cells may be further reduced. However,aspects of the present invention are not limited thereto.

Also, a communication system, such as a CoMP, enables blanking or mutingto be performed in an exemplary embodiment of FIG. 16, as describedabove with respect to FIGS. 10 to 12.

In order to avoid overlapping of description, a brief description willbe made as follows. In a cooperative multi-antennatransmission/reception system, such as a CoMP, in which a UE may receivea CSI-RS of a cell other than a serving cell, the UE may performblanking for leaving data blank without transmitting the data or mutingfor transmitting data with zero power with respect to REs through whichCSI-RSs are transmitted by a cell group other than a cell group, towhich the UE and the serving cell belong, among a total of 3 cellgroups.

FIG. 17 is an illustrative view showing a scheme for CSI-RS allocationin (FDM+CDM) according to an exemplary embodiment.

When a CSI-RS for each of a maximum of 8 antenna ports is allocated to atime-frequency domain in an exemplary embodiment of FIG. 17, a CSI-RSfor each of the 2 antenna ports is allocated to 2 REs or subcarrierswithin a first symbol (or symbol axis) in a first subframe or ResourceBlock (RB). Then, each of the CSI-RSs according to the 2 antenna ports,which have been allocated to the first symbol (or symbol axis), isequally allocated to 2 REs within a second symbol (or symbol axis) inthe same subframe. Consequently, a total of the 8 CSI-RS allocation REsare arranged in the first subframe or RB. Further, CSI-RSs according to2 antenna ports among the remaining 6 antenna ports excluding thepreviously-allocated 2 antenna ports, are distinguished from the CSI-RSsaccording to the previously-allocated 2 antenna ports by the OCC in thefirst subframe or RB. Then, each of the distinguished CSI-RSs accordingto the 2 antenna ports can be duplicately allocated to 4 CSI-RSallocation REs of the 8 CSI-RS allocation REs in the first subframe orRB. A CSI-RS for each of the remaining 4 antenna ports, which are notallocated to the first subframe, can be allocated to a second subframein the allocation scheme applied to the first subframe.

Namely, a CSI-RS for each of the 2 antenna ports is allocated to 2 REsof the 4 REs corresponding to 4 subcarriers among 12 subcarriers alongthe frequency axis within the first symbol in a single RB. At this time,a distance between the CSI-RSs allocated according to the 2 antennaports may be as long as 3 subcarriers. In the same scheme as describedabove, a CSI-RS for each of the 2 equal antenna ports is allocated toone of the 2 REs within the second symbol (or symbol axis) in the sameRB. In this case, a CSI-RS for each of a total of the 2 antenna ports isallocated to the 2 symbols in a single subframe. CSI-RSs according tothe 2 antenna ports excluding the previously-allocated 2 antenna portsare distinguished from the CSI-RSs according to the previously-allocated2 antenna ports by different codes, such as the OCC, which haveorthogonality, in the same subframe. For example, the CSI-RS antennaports 1 and 2 are mapped to the same RE in the same subframe, and thesame RE, which is allocated the CSI-RSs according to the CSI-RS antennaports 1 and 2, is transmitted. If the CSI-RSs according to the CSI-RSantenna ports 1 and 2 are allocated to the same RE, they aredistinguished by the OCC. The scheme as described above is similarlyapplied to the antenna ports 3 and 4. Also, a CSI-RS for each of theremaining 4 antenna ports (e.g., the CSI-RS antenna ports 5, 6, 7 and 8)is allocated to 2 symbols in another subframe in the scheme as describedabove. Therefore, the CSI-RSs are allocated to the 2 subframes among atotal of 10 subframes.

Referring to FIG. 17, the above allocation scheme will be described indetail as follows. CSI-RSs according to the antenna ports 1 and 2distinguished by the OCC are duplicately allocated to 2 REs located at(l, k)=(9 and 10, 0) in the first subframe. CSI-RSs according to theantenna ports 3 and 4 distinguished by the OCC are duplicately allocatedto 2 REs located at (l, k)=(9 and 10, 3) which is as distant as 3 REsfrom the location (9and 10, 0) in the direction of the frequency axis.CSI-RSs according to the antenna ports 1 and 2 distinguished by the OCCare duplicately allocated to 2 REs located at (l, k)=(9 and 10, 6) whichis as distant as 3 REs from the location (9 and 10, 3) in the directionof the frequency axis.

Consequently, a total of 4 REs are allocated CSI-RSs for each of 2antenna port sets, each of which includes 2 antenna ports among theantenna ports 1 to 4, in the first subframe. Therefore, the aboveallocation scheme satisfies the requirements of CSI-RS allocationoverhead such that a CSI-RS for each antenna port may be allocated to 2REs in a radio frame.

Further, a CSI-RS for each of the remaining 4 antenna ports 5 to 8 maybe allocated to another second subframe in the allocation scheme appliedto the first subframe.

At this time, there may be changes in numbers of antenna ports of whichCSI-RSs are duplicately allocated to the same RE (i.e., grouping ofantenna port sets), the order of antenna port numbers in the directionof the frequency axis, etc. In this regard, aspects of the presentinvention are not limited to the example of FIG. 17.

The CSI-RS mapping or allocation scheme according to aspects of thepresent invention as described above can be defined by equation (4)below. However, equation (4) expresses a representative example forpurposes of understanding of this embodiment, and may be differentlyexpressed while maintaining the basic scheme as described above.

CSI-RS antenna ports=1, 3, 5, 7: OCC [+1, +1]

CSI-RS antenna ports=2, 4, 6, 8: OCC [+1, −1]

Subframe A: transmission through CSI-RS antenna ports=1, 2, 3, 4

Subframe B: transmission through CSI-RS antenna ports=5, 6, 7, 8

$\begin{matrix}{{k = {{6 \cdot m} + {\left( {v + v_{shift}} \right){{mod}12}}}}{{l = 9},10}{{m = 0},1,2,\ldots\mspace{14mu},{{2 \cdot N_{RB}^{DL}} - 1}}{v = \left\{ {{\begin{matrix}0 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 1},2,7,8} \\3 & {{{{if}\mspace{14mu}{CSI}\text{-}{RS}\mspace{14mu}{antenna}\mspace{14mu}{ports}} = 3},4,5,6}\end{matrix}v_{shift}} = {N_{ID}^{cell}{mod}\; 6}} \right.}} & (4)\end{matrix}$

Herein, k represents a subcarrier number of an RE allocated a CSI-RS. lof an RE allocated a CSI-RS represents symbol (or symbol axis) numbers 0to 13.

Also, equation (4) defines 1 of an RE allocated a CSI-RS to have 9 or 10as a symbol (or symbol axis) number. However, aspects of the presentinvention are not limited thereto. Two optional symbols (or symbolaxes), which are adjacent or not adjacent, may be used among a total of14 symbols or symbol axes if a normal CP is used, and if an extended CPused, the number of symbols or symbol axes may be 12 or 6.

Further, as described above, there may be changes in numbers of antennaports of which CSI-RSs are duplicately allocated to the same RE, theorder of antenna port numbers in the direction of the frequency axis,etc. Aspects of the present invention are not limited to the example ofFIG. 17. Namely, in FIG. 17 and equation (4), the antenna ports, whichare allocated to the CSI-RS allocation REs in the first subframe, areindicated by (1, 2), (3, 4), (1, 2) and (3, 4) in the order of lowersubcarriers. However, aspects of the present invention are not limitedthereto. Also, in FIGS. 13 to 15, the antenna ports 1 to 4 are allocatedto the first subframe, and the antenna ports 5 to 8 are allocated to thesecond subframe. However, aspects of the present invention are notlimited thereto.

Here, the Orthogonal Cover Code (OCC) may be an optional code system,such as the 2-digit Walsh code system, in which codes have mutualorthogonality. Namely, in FIG. 17, a CSI-RS of an antenna port forwardindicated within each RE, for example, is distinguished by an OCC 1,such as [1, 1], and a CSI-RS of an antenna port backward indicatedwithin each RE, for example, is distinguished by an OCC 2, such as [1,−1], which is orthogonal to the OCC 1.

As illustrated in FIG. 17, the 2 antenna ports duplicately allocated to4 REs may be neighboring antenna ports. Namely, in FIG. 17, the 2antenna ports, which are duplicately allocated to (l, k)=(9 and 10, 0),neighboring antenna ports 1 and 2.

The first and second subframes may be optional in determining thelocations thereof but may have an appropriate distance therebetween in asingle radio frame. For example, if numbers of subframes included in theradio frame are defined to be 0 to 9 and the first subframe is locatedat the subframe number 1, the second subframe is arranged at thesubframe number 6 among the subframe numbers. However, aspects of thepresent invention are not limited thereto, and the first and secondsubframes may be adjacent or arranged differently.

Namely, CSI-RSs are allocated to 2 subframes among a total of 10subframes in consideration of CSI-RS allocation overhead. The 2subframes may be continuous or may have a specific period. Namely, the 2subframes having similar configurations are transmitted in the scheme ofFIG. 17. Therefore, the 2 subframes may be transmitted at intervals of 5ms, which is obtained by dividing a total of 10 ms by 2.

A scheme for alternate CSI-RS allocation between cells (or cell groups)can also be adopted in an exemplary embodiment of FIG. 17 similar to asillustrated in FIGS. 10 to 12.

Namely, according to equation (4), a scheme for CSI-RS allocation foreach antenna port may be similar to as illustrated in FIG. 17, and aCSI-RS for each antenna port is allocated in such a scheme as to haveoffsets or frequency shifts according to cells (or cell groups), eventhough the scheme is not shown in FIG. 17.

In other words, if at least one resource block is included, each antennaport allocates a CSI-RS to each 6^(th) subcarrier and transmits each6^(th) subcarrier allocated the CSI-RS in view of the entire frequencyaxis. Referring to FIG. 17, the CSI-RS antenna port 1, for example, ismapped to each (k=6·m)^(th) (m=0, 1, 2, . . . , 2·N_(RB) ^(DL)−1)subcarrier within the 10^(th) and 11^(th) symbols (having symbol numbersl=9 and 10) in a particular subframe. Herein, a total 6 of 0 to 5offsets or frequency shifts according to cell groups may be expressed byk=6 m+v_(shift) (m=0, 1, 2 . . . 2·N_(RB) ^(DL)−1). At this time, thereare different values of v_(shift) according to the cells. For example,v_(shift) may be expressed by v_(shift)=N_(ID) ^(cell) mod 6 accordingto Physical Cell Identities (PCIs), which are cell IDs.

If the 6 offsets or frequency shifts are also applied to each of otherantenna ports according to PCIs in the above scheme, a distance betweenCSI-RSs allocated for each of antenna ports may be as long as 3subcarriers. Therefore a total of 3 cell groups (a cell group A: N_(ID)^(cell) mod3=0, a cell group B: N_(ID) ^(cell) mod3=1, and a cell groupC: N_(ID) ^(cell) mod3=2) have perfectly-distinguished CSI-RS allocationpatterns with respect to time-frequency resources, respectively.

Namely, if the antenna port set (1, 2) is taken as an example, theCSI-RS allocation patterns signify a scheme in which the antenna portset (1, 2) is allocated to (l, k)=(9and 10, 0 and 6) (shown on the leftin FIG. 17 and N_(ID) ^(cell) mod3=0) in the first subframe in the cellgroup A, but the antenna port set (1, 2) is allocated to (l, k)=(9 and10, 1 and 7) (N_(ID) ^(cell) mod3=1) in the first subframe in the cellgroup B (not shown), and is allocated to (l, k)=(9 and 10, 2 and 8)(N_(ID) ^(cell) mod3=2) in the first subframe in the cell group C (notshown).

Also, the locations of the first and second subframes may be differentlyarranged for each cell group.

In other words, in the embodiment as described above, offsets orfrequency shifts according to cell groups may be applied to a locationof CSI-RS allocation in the direction of the frequency axis for eachantenna port in a single subframe, and thereby CSI-RS allocationpatterns may be differently defined among neighboring cells. However,further, subframes allocated CSI-RSs may be made different for eachneighboring cell.

For example, if the 2^(nd) and 7^(th) subframes, which have beenallocated CSI-RSs, among 10 subframes have been transmitted by aparticular cell group, the 3^(rd) and 8^(th) subframes are transmittedby another cell group. By making the relative locations of the first andsecond subframes different for each cell group in this manner,interference between neighboring cells may be further reduced. However,aspects of the present invention are not limited thereto.

Also, a communication system, such as a CoMP, enables blanking or mutingto be performed in an exemplary embodiment of FIG. 17, similar todescribed with respect to FIGS. 10 to 12.

In order to avoid overlapping of description, a brief description willbe made as follows. In a cooperative multi-antennatransmission/reception system, such as a CoMP, in which a UE may receivea CSI-RS of a cell other than a serving cell, the UE may performblanking for leaving data blank without transmitting the data or mutingfor transmitting data with zero power with respect to REs through whichCSI-RSs are transmitted by a cell group other than a cell group, towhich the UE and the serving cell belong, among a total of 3 cellgroups.

FIG. 18 is a block diagram illustrating the configuration of a receiverto receive a CSI-RS transmitted by a scheme for CSI-RS allocation andtransmission according an exemplary embodiment. Referring to FIG. 18, ina wireless communication system, a reception apparatus 1800 of a UEincludes a reception processing unit 1810, a resource element demapper1820, a CSI-RS extraction unit 1840, and a channel state measurementunit 1830, and may further include a decoding unit (not shown), acontrol unit, etc. (not shown). In this case, the reception apparatus1800 may be the UE 10 as illustrated in FIG. 1.

The reception processing unit 1810 receives a signal through eachantenna port of the reception apparatus 1800. The resource elementdemapper 1820 demaps information allocated to each Resource Element (RE)from the received signal. The demapped information may include controlinformation, and CSI-RSs and reference signals of various kindsaccording to multi-antenna ports other than data information.

The CSI-RS extraction unit 1840 may be included in the resource elementdemapper 1820 or may operate in connection with the resource elementdemapper 1820. When demapping information allocated to each RE, theresource element demapper 1820 demaps and extracts information relatedto the CSI-RSs. The CSI-RS extraction unit 1840 extracts CSI-RSinformation for each antenna port in reverse order of the scheme for theCSI-RS allocation in one of the schemes as shown in FIGS. 8 to 17. Thechannel state measurement unit 1830 measures, based on the extractedCSI-RS information, how the CSI-RS information is changed while theextracted CSI-RS information goes through a channel, and obtains ChannelSpatial Information (CSI) corresponding to channel state information foreach antenna port in a multi-antenna system including multiple antennas.

In other words, the CSI-RS extraction unit further includes that; theCSI-RS extraction unit extracts that, for the maximum N antenna ports (Nbeing an integer larger than or equal to 1) for transmission of theCSI-RS, the CSI-RS sequence is mapped to REs corresponding to onesub-carrier at every 12 sub-carriers for each antenna port with respectto two Orthogonal Frequency Division Multiplexing (OFDM) symbols withina sub-frame by which the CSI-RS is transmitted, for ┌N/2┐ antenna portsets, each of which includes either both an M^(th) (M≤N, and M being anodd number) antenna port and an (M+1)^(th) antenna port or only theM^(th) antenna port if the (M+1)^(th) antenna port does not exist and isused as an antenna port set for transmission of the CSI-RS, a CSI-RS ofantenna ports within each of the antenna port sets is allocated to REshaving the same time-frequency resource and are discriminated from eachother by orthogonal codes, and the CSI-RS allocated for two adjacentantenna port sets within a resource block are spaced apart from eachother with an interval of 3 REs in the frequency axis.

The reception apparatus 1800 makes a pair with or connects to thewireless communication system or the transmission apparatus 800 asdescribed above with reference to FIG. 8, and receives a signaltransmitted by the transmission apparatus 800. Therefore, the receptionapparatus 1800 includes elements for signal processing in the reverseprocess of signal processing of the transmission apparatus 800.Therefore, the reception apparatus 1800 may include elements for signalprocessing in the reverse process of signal processing of thetransmission apparatus 800.

FIG. 19 is a flowchart showing the flow of a CSI-RS transmission methodaccording to an exemplary embodiment. A CSI-RS transmission methodaccording to aspects of the present invention includes generating aCSI-RS or sequence for each antenna port in operation S1910, allocatinga CSI-RS for each antenna port to 4 REs or subcarrier on a basis of asingle symbol (or symbol axis) in a single subframe, and allocating theCSI-RS for each antenna port in such a manner that a distance betweenneighboring CSI-RS allocation REs or subcarriers may be as long as 3 REsor subcarriers in operation S1920, and transmitting CSI-RSs, which havebeen allocated to a time-frequency resource domain, to the receptionapparatus in operation S1930.

In operation S1920, a CSI-RS for a particular antenna port can beallocated in such a manner as to have frequency shifts in the directionof the frequency axis according to cells (or cell groups). Further, inoperation S1920, the CSI-RSs are allocated to 2 symbols (or symbol axes)in a single subframe or RB. At this time, a CSI-RS for each of a totalof 8 antenna ports is individually allocated to a single RE in a firstsubframe or RB. CSI-RSs according to antenna ports excluding thepreviously-allocated antenna ports are distinguished from CSI-RSsaccording to the previously-allocated antenna ports by using theOrthogonal Cover Code (OCC), and each of the distinguished CSI-RSsaccording to the antenna ports is duplicately allocated to 2 REs in afirst subframe or RB. The scheme as described above, which has beenapplied to the first subframe or RB, can be similarly applied to anotheror second subframe or RB to which a CSI-RS for each of a total of the 8antenna ports to be allocated.

Also, in operation S1920, the CSI-RSs are allocated to 2 symbols (orsymbol axes) in a single subframe or RB. At this time, a CSI-RS for eachof a total of 4 antenna ports is individually allocated to 2 REs in afirst subframe or RB. CSI-RSs according to antenna ports excluding thepreviously-allocated antenna ports are distinguished from CSI-RSsaccording to the previously-allocated antenna ports by using theOrthogonal Cover Code (OCC), and each of the distinguished CSI-RSsaccording to the antenna ports is duplicately allocated to 4 REs in afirst subframe or RB. The scheme as described above, which has beenapplied to the first subframe or RB, is similarly applied to another orsecond subframe or RB to which a CSI-RS for each of the remaining 4antenna ports excluding the 4 antenna ports allocated to the firstsubframe or RB is to be allocated.

A CSI-RS allocation method and a CSI-RS transmission method according toexemplary embodiments other than the exemplary embodiments as describedabove may use one of or all of the schemes as shown in FIGS. 8 to 17. Inorder to avoid overlapping of description, a detailed description willbe omitted.

According to aspects of the present invention, CSI-RSs are allocated toa time-frequency domain in such a manner as to have perfectorthogonality (in a CoMP) or quasi-orthogonality (in a non-CoMP)according to cells (or cell groups) in the range of following CSI-RStransmission overhead. As a result, performance degradation caused byinterference between neighboring cells can be reduced.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method for receiving a signal, comprising:receiving a signal comprising Channel State Information ReferenceSignals (CSI-RSs) for antenna ports in an antenna port set; andacquiring channel state information of a first antenna port in theantenna port set and channel state information of a second antenna portin the antenna port set based on the CSI-RSs, wherein the CSI-RSs forthe antenna ports in the antenna port set are mapped to 2 consecutiveResource Elements (REs) in a time-frequency resource area, thetime-frequency resource area being defined by one sub-frame and 12sub-carriers, and the 2 consecutive REs corresponding to 1 sub-carrierin a frequency axis and two symbols in a time axis, wherein the CSI-RSsfor the first antenna port and the second antenna port in the antennaport set are discriminated from each other by orthogonal codes includinga first orthogonal code for the first antenna port and a secondorthogonal code for the second antenna port, and wherein the firstorthogonal code is [1, 1], and the second orthogonal code is [1,−1]. 2.The method of claim 1, wherein the CSI-RSs correspond to first CSI-RSsand the antenna port set corresponds to a first antenna port set,wherein the signal further comprises second CSI-RSs for antenna ports ina second antenna port set, wherein the second CSI-RSs are mapped to 2consecutive REs in the time-frequency resource area different from the 2consecutive REs in which the first CSI-RSs are mapped, and wherein the 2consecutive REs in which the first CSI-RSs are mapped and the 2consecutive REs in which the second CSI-RSs are mapped are spaced apartfrom each other along the frequency axis.
 3. The method of claim 1,wherein a different between a number of the sub-carrier corresponding tothe 2 consecutive REs in which the first CSI-RSs are mapped and a numberof the sub-carrier corresponding to the 2 consecutive REs in which thesecond CSI-RSs are mapped is six.
 4. The method of claim 1, wherein thefirst antenna port and the second antenna port in the antenna port sethave consecutive antenna port numbers.
 5. The method of claim 1,wherein, if 4 antenna port sets including the antenna port set aredetermined for transmitting CSI-RSs, CSI-RSs for antenna ports in the 4antenna port sets are mapped to 8 REs, the 8 REs corresponding to 4evenly-spaced sub-carriers in a frequency axis and two symbols in a timeaxis, and wherein CSI-RSs for antenna ports in each antenna port set aremapped to 2 consecutive REs corresponding to one of the 4 evenly-spacedsub-carriers and the two symbols.
 6. A method for transmitting a signal,comprising: mapping Channel State Information Reference Signals(CSI-RSs) for antenna ports in an antenna port set to 2 consecutiveResource Elements (REs) in a time-frequency resource area, thetime-frequency resource area being defined by one sub-frame and 12sub-carriers, and the 2 consecutive REs corresponding to 1 sub-carrierin a frequency axis and two symbols in a time axis; generating a signalcomprising the mapped CSI-RSs; and transmitting the signal to a UserEquipment, wherein the CSI-RSs for a first antenna port and a secondantenna port in the antenna port set are discriminated from each otherby orthogonal codes including a first orthogonal code for the firstantenna port and a second orthogonal code for the second antenna port,and wherein the first orthogonal code is [1, 1], and the secondorthogonal code is [1, −1].
 7. The method of claim 6, wherein theCSI-RSs correspond to first CSI-RSs and the antenna port set correspondsto a first antenna port set, wherein the signal further comprises secondCSI-RSs for antenna ports in a second antenna port set, wherein thesecond CSI-RSs are mapped to 2 consecutive REs in the time-frequencyresource area different from the 2 consecutive REs in which the firstCSI-RSs are mapped, and wherein the 2 consecutive REs in which the firstCSI-RSs are mapped and the 2 consecutive REs in which the second CSI-RSsare mapped are spaced apart from each other along the frequency axis. 8.The method of claim 6, wherein a different between a number of thesub-carrier corresponding to the 2 consecutive REs in which the firstCSI-RSs are mapped and a number of the sub-carrier corresponding to the2 consecutive REs in which the second CSI-RSs are mapped is six.
 9. Themethod of claim 6, wherein the first antenna port and the second antennaport in the antenna port set have consecutive antenna port numbers. 10.The method of claim 6, wherein, if 4 antenna port sets including theantenna port set are determined for transmitting CSI-RSs, CSI-RSs forantenna ports in the 4 antenna port sets are mapped to 8 REs, the 8 REscorresponding to 4 evenly-spaced sub-carriers in a frequency axis andtwo symbols in a time axis, and wherein CSI-RSs for antenna ports ineach antenna port set are mapped to 2 consecutive REs corresponding toone of the 4 evenly-spaced sub-carriers and the two symbols.
 11. A UserEquipment (UE) to receive a signal, comprising: a receiver to receive asignal comprising Channel State Information Reference Signals (CSI-RSs)for antenna ports in an antenna port set; a processor to acquire channelstate information of a first antenna port in the antenna port set andchannel state information of a second antenna port in the antenna portset based on the CSI-RSs, wherein the CSI-RSs for the antenna ports inthe antenna port set are mapped to 2 consecutive Resource Elements (REs)in a time-frequency resource area, the time-frequency resource areabeing defined by one sub-frame and 12 sub-carriers, and the 2consecutive REs corresponding to 1 sub-carrier in a frequency axis andtwo symbols in a time axis, and wherein the CSI-RSs for the firstantenna port and the second antenna port in the antenna port set arediscriminated from each other by orthogonal codes including a firstorthogonal code for the first antenna port and a second orthogonal codefor the second antenna port, and wherein the first orthogonal code is[1, 1], and the second orthogonal code is [1, −1].
 12. The UE of claim11, wherein the CSI-RSs correspond to first CSI-RSs and the antenna portset corresponds to a first antenna port set, wherein the signal furthercomprises second CSI-RSs for antenna ports in a second antenna port set,wherein the second CSI-RSs are mapped to 2 consecutive REs in thetime-frequency resource area different from the 2 consecutive REs inwhich the first CSI-RSs are mapped, and wherein the 2 consecutive REs inwhich the first CSI-RSs are mapped and the 2 consecutive REs in whichthe second CSI-RSs are mapped are spaced apart from each other along thefrequency axis.
 13. The method of claim 12, wherein a different betweena number of the sub-carrier corresponding to the 2 consecutive REs inwhich the first CSI-RSs are mapped and a number of the sub-carriercorresponding to the 2 consecutive REs in which the second CSI-RSs aremapped is six.
 14. The UE of claim 11, wherein the first antenna portand the second antenna port in the antenna port set have consecutiveantenna port numbers.
 15. The UE of claim 11, wherein, if 4 antenna portsets including the antenna port set are determined for transmittingCSI-RSs, CSI-RSs for antenna ports in the 4 antenna port sets are mappedto 8 REs, the 8 REs corresponding to 4 evenly-spaced sub-carriers in afrequency axis and two symbols in a time axis, and wherein CSI-RSs forantenna ports in each antenna port set are mapped to 2 consecutive REscorresponding to one of the 4 evenly-spaced sub-carriers and the twosymbols.
 16. An evolved node B (eNodeB) to transmit a signal,comprising: a processor to map Channel State Information ReferenceSignals (CSI-RSs) for antenna ports in an antenna port set to 2consecutive Resource Elements (REs) in a time-frequency resource area,and to generate a signal comprising the mapped CSI-RSs, thetime-frequency resource area being defined by one sub-frame and 12sub-carriers, and the 2 consecutive REs corresponding to 1 sub-carrierin a frequency axis and two symbols in a time axis; and a transmitter totransmit the signal to a User Equipment, wherein the CSI-RSs for a firstantenna port and a second antenna port in the antenna port set arediscriminated from each other by orthogonal codes including a firstorthogonal code for the first antenna port and a second orthogonal codefor the second antenna port, and wherein the first orthogonal code is[1, 1], and the second orthogonal code is [1, −1].
 17. The eNodeB ofclaim 16, wherein the CSI-RSs correspond to first CSI-RSs and theantenna port set corresponds to a first antenna port set, wherein thesignal further comprises second CSI-RSs for antenna ports in a secondantenna port set, wherein the second CSI-RSs are mapped to 2 consecutiveREs in the time-frequency resource area different from the 2 consecutiveREs in which the first CSI-RSs are mapped, and wherein the 2 consecutiveREs in which the first CSI-RSs are mapped and the 2 consecutive REs inwhich the second CSI-RSs are mapped are spaced apart from each otheralong the frequency axis.
 18. The method of claim 17, wherein adifferent between a number of the sub-carrier corresponding to the 2consecutive REs in which the first CSI-RSs are mapped and a number ofthe sub-carrier corresponding to the 2 consecutive REs in which thesecond CSI-RSs are mapped is six.
 19. The eNodeB of claim 16, whereinthe first antenna port and the second antenna port in the antenna portset have consecutive antenna port numbers.
 20. The eNodeB of claim 16,wherein, if 4 antenna port sets including the antenna port set aredetermined for transmitting CSI-RSs, CSI-RSs for antenna ports in the 4antenna port sets are mapped to 8 REs, the 8 REs corresponding to 4evenly-spaced sub-carriers in a frequency axis and two symbols in a timeaxis, and wherein CSI-RSs for antenna ports in each antenna port set aremapped to 2 consecutive REs corresponding to one of the 4 evenly-spacedsub-carriers and the two symbols.